ADC14L020EVAL

ADC14L020 14-Bit, 20 MSPS, 150 mW A/D Converter March 2006 ADC14L020 14-Bit, 20 MSPS, 150 mW A/D Converter General Description The ADC14L020 is a low power monolithic CMOS analogto-digital converter capable of converting analog input signals into 14-bit digital words at 20 Megasamples per second (MSPS). This converter uses a differential, pipeline architecture with digital error correction and an on-chip sample-andhold circuit to minimize power consumption while providing excellent dynamic performance and a 150 MHz Full Power Bandwidth. Operating on a single +3.3V power supply, the ADC14L020 achieves 12.0 effective bits at nyquist and consumes just 150 mW at 20 MSPS . The Power Down feature reduces power consumption to 15 mW. The differential inputs provide a full scale differential input swing equal to 2 times VREF with the possibility of a singleended input. Full use of the differential input is recommended for optimum performance. Duty cycle stabilization and output data format are selectable using a quad state function pin. The output data can be set for offset binary or two’s complement. To ease interfacing to lower voltage systems, the digital output driver power pins of the ADC14L020 can be connected to a separate supply voltage in the range of 2.4V to the analog supply voltage. This device is available in the 32-lead LQFP package and will operate over the industrial temperature range of −40˚C to +85˚C. An evaluation board is available to ease the evaluation process. Features n n n n n n Single +3.3V supply operation Internal sample-and-hold Internal reference Outputs 2.4V to 3.6V compatible Duty Cycle Stabilizer Power down mode Key Specifications n n n n n n n n Resolution DNL SNR (fIN = 10 MHz) SFDR (fIN = 10 MHz) Data Latency Power Consumption -- Operating -- Power Down Mode 14 Bits ± 0.5 LSB (typ) 74 dB (typ) 93 dB (typ) 7 Clock Cycles 150 mW (typ) 15 mW (typ) Applications n n n n Medical Imaging Instrumentation Communications Digital Video Connection Diagram 20157001 © 2006 National Semiconductor Corporation DS201570 www.national.com ADC14L020 Ordering Information Industrial (−40˚C ≤ TA ≤ +85˚C) ADC14L020CIVY ADC14L020EVAL Package 32 Pin LQFP Evaluation Board Block Diagram 20157002 www.national.com 2 ADC14L020 Pin Descriptions and Equivalent Circuits Pin No. ANALOG I/O Differential analog input pins. With a 1.0V reference voltage the differential full-scale input signal level is 2.0 VP-P with each input pin voltage centered on a common mode voltage, VCM. The negative input pins may be connected to VCM for single-ended operation, but a differential input signal is required for best performance. Symbol Equivalent Circuit Description 2 VIN+ 3 VIN− 1 VREF This pin is the reference select pin and the external reference input. If (VA - 0.3V) < VREF < VA, the internal 1.0V reference is selected. If AGND < VREF < (AGND + 0.3V), the internal 0.5V reference is selected. If a voltage in the range of 0.4V to (VA - 0.4V) is applied to this pin, that voltage is used as the reference. The full scale differential voltage range is 2 * VREF. VREF should be bypassed to AGND with a 0.1 µF capacitor when an external reference is used. 31 VRP These pins should each be bypassed to AGND with a low ESL (equivalent series inductance) 0.1 µF capacitor. A 10 µF capacitor should be placed between the VRP and VRN. VRM may be loaded to 1mA for use as a temperature stable 1.5V reference. The remaining pins should not be loaded. VRM may be used to provide the common mode voltage, VCM, for the differential inputs. 32 VRM 30 VRN 11 DF/DCS This is a four-state pin. DF/DCS = VA, output data format is offset binary with duty cycle stabilization applied to the input clock DF/DCS = AGND, output data format is 2’s complement, with duty cycle stabilization applied to the input clock. DF/DCS = VRM , output data is 2’s complement without duty cycle stabilization applied to the input clock DF/DCS = "float", output data is offset binary without duty cycle stabilization applied to the input clock. Digital clock input. The range of frequencies for this input is as specified in the electrical tables with guaranteed performance at 20 MHz. The input is sampled on the rising edge. PD is the Power Down input pin. When high, this input puts the converter into the power down mode. When this pin is low, the converter is in the active mode. DIGITAL I/O 10 CLK 8 PD 3 www.national.com ADC14L020 Pin Descriptions and Equivalent Circuits Pin No. Symbol Equivalent Circuit (Continued) Description 12-19 22-27 D0–D13 Digital data output pins that make up the 14-bit conversion result. D0 (pin 12) is the LSB, while D13 (pin 27) is the MSB of the output word. Output levels are TTL/CMOS compatible. Optimum loading is < 10pF. ANALOG POWER Positive analog supply pins. These pins should be connected to a quiet +3.3V source and bypassed to AGND with 0.1 µF capacitors located close to these power pins, and with a 10 µF capacitor. The ground return for the analog supply. Positive digital supply pin. This pin should be connected to the same quiet +3.3V source as is VA and be bypassed to DGND with a 0.1 µF capacitor located close to the power pin and with a 10 µF capacitor. The ground return for the digital supply. Positive driver supply pin for the ADC14L020’s output drivers. This pin should be connected to a voltage source of +2.4V to VD and be bypassed to DR GND with a 0.1 µF capacitor. If the supply for this pin is different from the supply used for VA and VD, it should also be bypassed with a 10 µF capacitor. VDR should never exceed the voltage on VD. All 0.1 µF bypass capacitors should be located close to the supply pin. The ground return for the digital supply for the ADC’s output drivers. These pins should be connected to the system digital ground, but not be connected in close proximity to the ADC’s DGND or AGND pins. See Section 5 (Layout and Grounding) for more details. 5, 29 VA 4, 7, 28 DIGITAL POWER AGND 6 VD 9 DGND 21 VDR 20 DR GND www.national.com 4 ADC14L020 Absolute Maximum Ratings 2) (Notes 1, Operating Ratings (Notes 1, 2) Operating Temperature Supply Voltage (VA, VD) Output Driver Supply (VDR) CLK, PD Clock Duty Cycle (DCS On) Clock Duty Cycle (DCS Off) Analog Input Pins VCM |AGND–DGND| −40˚C ≤ TA ≤ +85˚C +3.0V to +3.6V +2.4V to VD −0.05V to (VD + 0.05V) 20% to 80% 40% to 60% 0V to 2.6V 0.5V to 2.0V ≤100mV If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VA, VD, VDR |VA–VD| Voltage on Any Input or Output Pin Input Current at Any Pin (Note 3) Package Input Current (Note 3) Package Dissipation at TA = 25˚C ESD Susceptibility Human Body Model (Note 5) Machine Model (Note 5) Storage Temperature 2500V 250V −65˚C to +150˚C 4.2V ≤ 100 mV −0.3V to (VA or VD +0.3V) ± 25 mA ± 50 mA See (Note 4) Soldering process must comply with National Semiconductor’s Reflow Temperature Profile specifications. Refer to www.national.com/packaging. (Note 6) Converter Electrical Characteristics Unless otherwise specified, the following specifications apply for AGND = DGND = DR GND = 0V, VA = VD = +3.3V, VDR = +2.5V, PD = 0V, External VREF = +1.0V, fCLK = 20 MHz, fIN = 10 MHz at -0.5dBFS, tr = tf = 2 ns, CL = 15 pF/pin, Duty Cycle Stabilizer On. Boldface limits apply for TJ = TMIN to TMAX: all other limits TJ = 25˚C (Notes 7, 8, 9) Symbol Parameter Conditions Typical Limits (Note 10) (Note 10) 14 Units (Limits) Bits (min) LSB (max) LSB (max) %FS (max) %FS (max) ppm/˚C %FS (max) ppm/˚C 0 16383 0.5 2.0 V (min) V (max) V pF pF 0.8 1.2 V (min) V (max) MΩ (min) STATIC CONVERTER CHARACTERISTICS Resolution with No Missing Codes INL DNL PGE NGE TC GE VOFF TC VOFF Integral Non Linearity (Note 11) Differential Non Linearity Positive Gain Error Negative Gain Error Gain Error Tempco Offset Error (VIN+ = VIN−) Offset Error Tempco Under Range Output Code Over Range Output Code REFERENCE AND ANALOG INPUT CHARACTERISTICS VCM VRM CIN VREF Common Mode Input Voltage Reference Output Voltage VIN Input Capacitance (each pin to GND) External Reference Voltage (Note 13) Reference Input Resistance Output load = 1 mA VIN = 1.5 Vdc ± 0.5 V (CLK LOW) (CLK HIGH) 1.5 1.5 11 4.5 1.00 1 −40˚C ≤ TA ≤ +85˚C −40˚C ≤ TA ≤ +85˚C ± 1.4 ± 0.5 0.3 0.3 2.5 -0.06 1.5 ± 3.8 ± 1.0 ± 3.3 ± 3.3 ± 0.85 5 www.national.com ADC14L020 Converter Electrical Characteristics (Continued) Unless otherwise specified, the following specifications apply for AGND = DGND = DR GND = 0V, VA = VD = +3.3V, VDR = +2.5V, PD = 0V, External VREF = +1.0V, fCLK = 20 MHz, fIN = 10 MHz at -0.5dBFS, tr = tf = 2 ns, CL = 15 pF/pin, Duty Cycle Stabilizer On. Boldface limits apply for TJ = TMIN to TMAX: all other limits TJ = 25˚C (Notes 7, 8, 9) Symbol Parameter Conditions Typical Limits (Note 10) (Note 10) 150 74 74 74 74 12 12 -90 -90 -97 -97 -96 -96 93 93 −76 81 -81 -81 -80 11.7 72.2 72.3 Units (Limits) MHz dBc dBc dBc dBc Bits Bits dBc dBc dBc dBc dBc dBc dBc dBc dBFS DYNAMIC CONVERTER CHARACTERISTICS FPBW SNR SINAD ENOB THD H2 H3 SFDR IMD Full Power Bandwidth Signal-to-Noise Ratio Signal-to-Noise Ratio and Distortion Effective Number of Bits Total Harmonic Disortion Second Harmonic Distortion Third Harmonic Distortion Spurious Free Dynamic Range Intermodulation Distortion 0 dBFS Input, Output at −3 dB fIN = 1 MHz fIN =10 MHz fIN = 1 MHz fIN = 10 MHz fIN = 1 MHz fIN = 10 MHz fIN = 1 MHz fIN = 10 MHz fIN = 1 MHz fIN = 10 MHz fIN = 1 MHz fIN = 10 MHz fIN = 1 MHz fIN = 10 MHz fIN = 4.8 MHz and 5.2 MHz, each = −6.5 dBFS DC and Logic Electrical Characteristics Unless otherwise specified, the following specifications apply for AGND = DGND = DR GND = 0V, VA = VD = +3.3V, VDR = +2.5V, PD = 0V, External VREF = +1.0V, fCLK = 20 MHz, fIN = 10 MHz, tr = tf = 2 ns, CL = 15 pF/pin, Duty Cycle Stabilizer On. Boldface limits apply for TJ = TMIN to TMAX: all other limits TJ = 25˚C (Notes 7, 8, 9) Symbol Parameter Conditions Typical (Note 10) Limits (Note 10) 2.0 1.0 10 −10 5 VDR = 2.5V VDR = 3V 2.3 2.7 0.4 −10 10 5 PD Pin = DGND, VREF = VA PD Pin = VD PD Pin = DGND PD Pin = VD , fCLK = 0 PD Pin = DGND, CL = 5 pF (Note 14) PD Pin = VD, fCLK = 0 PD Pin = DGND, CL = 5 pF (Note 15) 6 Units (Limits) V (min) V (max) µA µA pF V (min) V (min) V (max) mA mA pF CLK, PD DIGITAL INPUT CHARACTERISTICS VIN(1) VIN(0) IIN(1) IIN(0) CIN Logical “1” Input Voltage Logical “0” Input Voltage Logical “1” Input Current Logical “0” Input Current Digital Input Capacitance VD = 3.6V VD = 3.0V VIN = 3.3V VIN = 0V D0–D13 DIGITAL OUTPUT CHARACTERISTICS VOUT(1) VOUT(0) +ISC −ISC COUT Logical “1” Output Voltage Logical “0” Output Voltage Output Short Circuit Source Current Output Short Circuit Sink Current Digital Output Capacitance IOUT = −0.5 mA IOUT = 1.6 mA, VDR = 3V VOUT = 0V VOUT = VDR POWER SUPPLY CHARACTERISTICS IA ID IDR Analog Supply Current Digital Supply Current Digital Output Supply Current Total Power Consumption www.national.com 41 4.5 4.5 0 2.5 0 150 57 8 mA (max) mA mA (max) mA mA mA 215 mW (max) ADC14L020 DC and Logic Electrical Characteristics (Continued) Unless otherwise specified, the following specifications apply for AGND = DGND = DR GND = 0V, VA = VD = +3.3V, VDR = +2.5V, PD = 0V, External VREF = +1.0V, fCLK = 20 MHz, fIN = 10 MHz, tr = tf = 2 ns, CL = 15 pF/pin, Duty Cycle Stabilizer On. Boldface limits apply for TJ = TMIN to TMAX: all other limits TJ = 25˚C (Notes 7, 8, 9) Symbol Parameter Power Down Power Consumption PSRR Power Supply Rejection Ratio Conditions PD Pin = VD, clock on Rejection of Full-Scale Error with VA =3.0V vs. 3.6V Typical (Note 10) 15 72 Limits (Note 10) Units (Limits) mW dB AC Electrical Characteristics Unless otherwise specified, the following specifications apply for AGND = DGND = DR GND = 0V, VA = VD = +3.3V, VDR = +2.5V, PD = 0V, External VREF = +1.0V, fCLK = 20 MHz, fIN = 10 MHz, tr = tf = 2 ns, CL = 15 pF/pin, Duty Cycle Stabilizer On. Boldface limits apply for TJ = TMIN to TMAX: all other limits TJ = 25˚C (Notes 7, 8, 9, 12) Symbol fCLK1 fCLK2 tCH tCL tCH tCL tCONV tOD tAD tAJ tPD Parameter Maximum Clock Frequency Minimum Clock Frequency Clock High Time Clock Low Time Clock High Time Clock Low Time Conversion Latency Data Output Delay after Rising Clock Edge Aperture Delay Aperture Jitter Power Down Mode Exit Cycle 0.1 µF on pins 30, 31, 32; 10 µF between pins 30, 31 6 2 0.7 280 Duty Cycle Stabilizer On Duty Cycle Stabilizer On Duty Cycle Stabilizer Off Duty Cycle Stabilizer Off 5 25 25 25 25 10 10 20 20 7 9.6 Conditions Typical (Note 10) Limits (Note 10) 20 Units (Limits) MHz (min) MHz ns (min) ns (min) ns (min) ns (min) Clock Cycles ns (max) ns ps rms µs Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions. Note 2: All voltages are measured with respect to GND = AGND = DGND = 0V, unless otherwise specified. Note 3: When the input voltage at any pin exceeds the power supplies (that is, VIN < AGND, or VIN > VA), the current at that pin should be limited to 25 mA. The 50 mA maximum package input current rating limits the number of pins that can safely exceed the power supplies with an input current of 25 mA to two. Note 4: The absolute maximum junction temperature (TJmax) for this device is 150˚C. The maximum allowable power dissipation is dictated by TJmax, the junction-to-ambient thermal resistance (θJA), and the ambient temperature, (TA), and can be calculated using the formula PDMAX = (TJmax - TA )/θJA. The values for maximum power dissipation listed above will be reached only when the device is operated in a severe fault condition (e.g. when input or output pins are driven beyond the power supply voltages, or the power supply polarity is reversed). Obviously, such conditions should always be avoided. Note 5: Human body model is 100 pF capacitor discharged through a 1.5 kΩ resistor. Machine model is 220 pF discharged through 0Ω. Note 6: Reflow temperature profiles are different for lead-free and non-lead-free packages. Note 7: The inputs are protected as shown below. Input voltage magnitudes above VA or below GND will not damage this device, provided current is limited per (Note 3). However, errors in the A/D conversion can occur if the input goes above VA or below GND by more than 100 mV. As an example, if VA is +3.3V, the full-scale input voltage must be ≤+3.4V to ensure accurate conversions. 20157011 Note 8: To guarantee accuracy, it is required that |VA–VD| ≤ 100 mV and separate bypass capacitors are used at each power supply pin. Note 9: With the test condition for VREF = +1.0V (2VP-P differential input), the 14-bit LSB is 122.1 µV. Note 10: Typical figures are at TJ = 25˚C, and represent most likely parametric norms. Test limits are guaranteed to National’s AOQL (Average Outgoing Quality Level). 7 www.national.com ADC14L020 AC Electrical Characteristics (Continued) Note 11: Integral Non Linearity is defined as the deviation of the analog value, expressed in LSBs, from the straight line that passes through positive and negative full-scale. Note 12: Timing specifications are tested at TTL logic levels, VIL = 0.4V for a falling edge and VIH = 2.4V for a rising edge. Note 13: Optimum performance will be obtained by keeping the reference input in the 0.8V to 1.2V range. The LM4051CIM3-ADJ (SOT-23 package) is recommended for external reference applications. Note 14: IDR is the current consumed by the switching of the output drivers and is primarily determined by load capacitance on the output pins, the supply voltage, VDR, and the rate at which the outputs are switching (which is signal dependent). IDR=VDR(C0 x f0 + C1 x f1 +....C11 x f11) where VDR is the output driver power supply voltage, Cn is total capacitance on the output pin, and fn is the average frequency at which that pin is toggling. Note 15: Excludes IDR. See note 14. www.national.com 8 ADC14L020 Specification Definitions APERTURE DELAY is the time after the rising edge of the clock to when the input signal is acquired or held for conversion. APERTURE JITTER (APERTURE UNCERTAINTY) is the variation in aperture delay from sample to sample. Aperture jitter manifests itself as noise in the output. CLOCK DUTY CYCLE is the ratio of the time during one cycle that a repetitive digital waveform is high to the total time of one period. The specification here refers to the ADC clock input signal. COMMON MODE VOLTAGE (VCM) is the common d.c. voltage applied to both input terminals of the ADC. CONVERSION LATENCY is the number of clock cycles between initiation of conversion and when that data is presented to the output driver stage. Data for any given sample is available at the output pins the Pipeline Delay plus the Output Delay after the sample is taken. New data is available at every clock cycle, but the data lags the conversion by the pipeline delay. DIFFERENTIAL NON-LINEARITY (DNL) is the measure of the maximum deviation from the ideal step size of 1 LSB. EFFECTIVE NUMBER OF BITS (ENOB, or EFFECTIVE BITS) is another method of specifying Signal-to-Noise and Distortion or SINAD. ENOB is defined as (SINAD - 1.76) / 6.02 and says that the converter is equivalent to a perfect ADC of this (ENOB) number of bits. FULL POWER BANDWIDTH is a measure of the frequency at which the reconstructed output fundamental drops 3 dB below its low frequency value for a full scale input. GAIN ERROR is the deviation from the ideal slope of the transfer function. It can be calculated as: Gain Error = Positive Full Scale Error − Negative Full Scale Error It can also be expressed as Positive Gain Error and Negative Gain Error, which are calculated as: PGE = Positive Full Scale Error - Offset Error NGE = Offset Error - Negative Full Scale Error INTEGRAL NON LINEARITY (INL) is a measure of the deviation of each individual code from a line drawn from negative full scale (1⁄2 LSB below the first code transition) through positive full scale (1⁄2 LSB above the last code transition). The deviation of any given code from this straight line is measured from the center of that code value. INTERMODULATION DISTORTION (IMD) is the creation of additional spectral components as a result of two sinusoidal frequencies being applied to the ADC input at the same time. It is defined as the ratio of the power in the intermodulation products to the total power in the original frequencies. IMD is usually expressed in dBFS. LSB (LEAST SIGNIFICANT BIT) is the bit that has the smallest value or weight of all bits. This value is VFS/2n, where “VFS” is the full scale input voltage and “n” is the ADC resolution in bits. MISSING CODES are those output codes that will never appear at the ADC outputs. The ADC14L020 is guaranteed not to have any missing codes. MSB (MOST SIGNIFICANT BIT) is the bit that has the largest value or weight. Its value is one half of full scale. NEGATIVE FULL SCALE ERROR is the difference between the actual first code transition and its ideal value of 1⁄2 LSB above negative full scale. OFFSET ERROR is the difference between the two input voltages [(VIN+) – (VIN-)] required to cause a transition from code 8191 to 8192. OUTPUT DELAY is the time delay after the rising edge of the clock before the data update is presented at the output pins. PIPELINE DELAY (LATENCY) See CONVERSION LATENCY. POSITIVE FULL SCALE ERROR is the difference between the actual last code transition and its ideal value of 11⁄2 LSB below positive full scale. POWER SUPPLY REJECTION RATIO (PSRR) is a measure of how well the ADC rejects a change in the power supply voltage. PSRR is the ratio of the change in Full-Scale Error that results from a change in the d.c. power supply voltage, expressed in dB. SIGNAL TO NOISE RATIO (SNR) is the ratio, expressed in dB, of the rms value of the input signal to the rms value of the sum of all other spectral components below one-half the sampling frequency, not including harmonics or d.c. SIGNAL TO NOISE PLUS DISTORTION (S/N+D or SINAD) Is the ratio, expressed in dB, of the rms value of the input signal to the rms value of all of the other spectral components below half the clock frequency, including harmonics but excluding d.c. SPURIOUS FREE DYNAMIC RANGE (SFDR) is the difference, expressed in dB, between the rms values of the input signal and the peak spurious signal, where a spurious signal is any signal present in the output spectrum that is not present at the input. TOTAL HARMONIC DISTORTION (THD) is the ratio, expressed in dB, of the rms total of the first nine harmonic levels at the output to the level of the fundamental at the output. THD is calculated as where f1 is the RMS power of the fundamental (output) frequency and f2 through f10 are the RMS power of the first 9 harmonic frequencies in the output spectrum. SECOND HARMONIC DISTORTION (2ND HARM) is the difference expressed in dB, between the RMS power in the input frequency at the output and the power in its 2nd harmonic level at the output. THIRD HARMONIC DISTORTION (3RD HARM) is the difference, expressed in dB, between the RMS power in the input frequency at the output and the power in its 3rd harmonic level at the output. 9 www.national.com ADC14L020 Timing Diagram 20157009 Output Timing Transfer Characteristic 20157010 FIGURE 1. Transfer Characteristic www.national.com 10 ADC14L020 Typical Performance Characteristics, DNL, INL Unless otherwise specified, the following specifications apply for AGND = DGND = DR GND = 0V, VA = VD = +3.3V, VDR = +2.5V, PD = 0V, External VREF = +1.0V, fCLK = 20 MHz, fIN = 0 MHz, tr = tf = 2 ns, CL = 15 pF/pin, Duty Cycle Stabilizer On. Boldface limits apply for TJ = TMIN to TMAX: all other limits TJ = 25˚C DNL INL 20157061 20157062 DNL vs. fCLK INL vs. fCLK 20157063 20157064 DNL vs. Clock Duty Cycle INL vs. Clock Duty Cycle 20157065 20157066 11 www.national.com ADC14L020 Typical Performance Characteristics, DNL, INL Unless otherwise specified, the following specifications apply for AGND = DGND = DR GND = 0V, VA = VD = +3.3V, VDR = +2.5V, PD = 0V, External VREF = +1.0V, fCLK = 20 MHz, fIN = 0 MHz, tr = tf = 2 ns, CL = 15 pF/pin, Duty Cycle Stabilizer On. Boldface limits apply for TJ = TMIN to TMAX: all other limits TJ = 25˚C (Continued) DNL vs. Temperature INL vs. Temperature 20157067 20157068 DNL vs. VDR, VA = VD = 3.6V INL vs. VDR, VA = VD = 3.6V 20157069 20157070 www.national.com 12 ADC14L020 Typical Performance Characteristics Unless otherwise specified, the following specifications apply for AGND = DGND = DR GND = 0V, VA = VD = +3.3V, VDR = +2.5V, PD = 0V, External VREF = +1.0V, fCLK = 20 MHz, fIN = 10 MHz, tr = tf = 2 ns, CL = 15 pF/pin, Duty Cycle Stabilizer On. Boldface limits apply for TJ = TMIN to TMAX: all other limits TJ = 25˚C SNR,SINAD,SFDR vs. VA Distortion vs. VA 20157071 20157072 SNR,SINAD,SFDR vs. VDR, VA = VD = 3.6V Distortion vs. VDR, VA = VD = 3.6V 20157073 20157074 SNR,SINAD,SFDR vs. VCM Distortion vs. VCM 20157075 20157076 13 www.national.com ADC14L020 Typical Performance Characteristics Unless otherwise specified, the following specifications apply for AGND = DGND = DR GND = 0V, VA = VD = +3.3V, VDR = +2.5V, PD = 0V, External VREF = +1.0V, fCLK = 20 MHz, fIN = 10 MHz, tr = tf = 2 ns, CL = 15 pF/pin, Duty Cycle Stabilizer On. Boldface limits apply for TJ = TMIN to TMAX: all other limits TJ = 25˚C (Continued) SNR,SINAD,SFDR vs. fCLK Distortion vs. fCLK 20157077 20157078 SNR,SINAD,SFDR vs. Clock Duty Cycle Distortion vs. Clock Duty Cycle 20157079 20157080 SNR,SINAD,SFDR vs. VREF Distortion vs. VREF 20157081 20157082 www.national.com 14 ADC14L020 Typical Performance Characteristics Unless otherwise specified, the following specifications apply for AGND = DGND = DR GND = 0V, VA = VD = +3.3V, VDR = +2.5V, PD = 0V, External VREF = +1.0V, fCLK = 20 MHz, fIN = 10 MHz, tr = tf = 2 ns, CL = 15 pF/pin, Duty Cycle Stabilizer On. Boldface limits apply for TJ = TMIN to TMAX: all other limits TJ = 25˚C (Continued) SNR,SINAD,SFDR vs. fIN Distortion vs. fIN 20157083 20157084 SNR,SINAD,SFDR vs. Temperature Distortion vs. Temperature 20157085 20157086 tOD vs. VDR, VA = VD = 3.6V Spectral Response @ 2.4 MHz Input 20157087 20157088 15 www.national.com ADC14L020 Typical Performance Characteristics Unless otherwise specified, the following specifications apply for AGND = DGND = DR GND = 0V, VA = VD = +3.3V, VDR = +2.5V, PD = 0V, External VREF = +1.0V, fCLK = 20 MHz, fIN = 10 MHz, tr = tf = 2 ns, CL = 15 pF/pin, Duty Cycle Stabilizer On. Boldface limits apply for TJ = TMIN to TMAX: all other limits TJ = 25˚C (Continued) Spectral Response @ 4.4 MHz Input Spectral Response @ 10 MHz Input 20157089 20157090 Intermodulation Distortion, fIN1= 4.8 MHz, fIN2 = 5.2 MHz Histogram with input grounded 20157091 20157092 www.national.com 16 ADC14L020 Functional Description Operating on a single +3.3V supply, the ADC14L020 uses a pipeline architecture and has error correction circuitry to help ensure maximum performance. The differential analog input signal is digitized to 14 bits. The user has the choice of using an internal 1.0 Volt or 0.5 Volt stable reference, or using an external reference. Any external reference is buffered onchip to ease the task of driving that pin. The output word rate is the same as the clock frequency. For the ADC14L020 the clock frequency can be between 5 MSPS and 20 MSPS (typical) with fully specified performance at 20 MSPS. The analog input is acquired at the rising edge of the clock and the digital data for a given sample is delayed by the pipeline for 7 clock cycles. Duty cycle stablization and output data format are selectable using the quad state function DF/DCS pin. The output data can be set for offset binary or two’s complement. A logic high on the power down (PD) pin reduces the converter power consumption to 15 mW. Smaller capacitor values than those specified will allow faster recovery from the power down mode, but may result in degraded noise performance. Loading any of these pins other than VRM may result in performance degradation. The nominal voltages for the reference bypass pins are as follows: VRM = 1.5 V VRP = VRM + VREF / 2 VRN = VRM − VREF / 2 User choice of an on-chip or external reference voltage is provided. The internal 1.0 Volt reference is in use when the the VREF pin is connected to VA. When the VREF pin is connected to AGND, the internal 0.5 Volt reference is in use. If a voltage in the range of 0.8V to 1.2V is applied to the VREF pin, that is used for the voltage reference. When an external reference is used, the VREF pin should be bypassed to ground with a 0.1 µF capacitor close to the reference input pin. There is no need to bypass the VREF pin when the internal reference is used. 1.3 Signal Inputs The signal inputs are VIN + and VIN− . The input signal, VIN, is defined as VIN = (VIN+) – (VIN−) Figure 2 shows the expected input signal range. Note that the common mode input voltage, VCM, should be in the range of 0.5V to 2.0V. The peaks of the individual input signals should each never exceed 2.6V. The ADC14L020 performs best with a differential input signal with each input centered around a common mode voltage, VCM. The peak-to-peak voltage swing at each analog input pin should not exceed the value of the reference voltage or the output data will be clipped. The two input signals should be exactly 180˚ out of phase from each other and of the same amplitude. For single frequency inputs, angular errors result in a reduction of the effective full scale input. For complex waveforms, however, angular errors will result in distortion. Applications Information 1.0 OPERATING CONDITIONS We recommend that the following conditions be observed for operation of the ADC14L020: 3.0V ≤ VA ≤ 3.6V VD = V A 2.4V ≤ VDR ≤ VA 5 MHz ≤ fCLK ≤ 20 MHz 0.8V ≤ VREF ≤ 1.2V (for an external reference) 0.5V ≤ VCM ≤ 2.0V 1.1 Analog Inputs There is one reference input pin, VREF, which is used to select an internal reference, or to supply an external reference. The ADC14L020 has one analog signal input pairs, VIN + and VIN - . This pair of pins forms a differential input pair. 1.2 Reference Pins The ADC14L020 is designed to operate with an internal 1.0V or 0.5V reference, or an external 1.0V reference, but performs well with external reference voltages in the range of 0.8V to 1.2V. Lower reference voltages will decrease the signal-to-noise ratio (SNR) of the ADC14L020. Increasing the reference voltage (and the input signal swing) beyond 1.2V may degrade THD for a full-scale input, especially at higher input frequencies. It is important that all grounds associated with the reference voltage and the analog input signal make connection to the ground plane at a single, quiet point to minimize the effects of noise currents in the ground path. The Reference Bypass Pins (VRP, VRM, and VRN) are made available for bypass purposes. All these pins should each be bypassed to ground with a 0.1 µF capacitor. A 10 µF capacitor should be placed between the VRP and VRN pins, as shown in Figure 4. This configuration is necessary to avoid reference oscillation, which could result in reduced SFDR and/or SNR. VRM may be loaded to 1mA for use as a temperature stable 1.5V reference. The remaining pins should not be loaded. 20157015 FIGURE 2. Expected Input Signal Range For single frequency sine waves the full scale error in LSB can be described as approximately EFS = 16384 ( 1 - sin (90˚ + dev)) Where dev is the angular difference in degrees between the two signals having a 180˚ relative phase relationship to each other (see Figure 3). Drive the analog inputs with a source impedance less than 100Ω. 17 www.national.com ADC14L020 Applications Information (Continued) VIN+ VCM − VREF/2 VCM VCM + VREF/2 VIN− VCM VCM VCM VCM Binary Output 01 0000 0000 0000 10 0000 0000 0000 11 0000 0000 0000 11 1111 1111 1111 2’s Complement Output 11 0000 0000 0000 00 0000 0000 0000 01 0000 0000 0000 01 1111 1111 1111 20157016 FIGURE 3. Angular Errors Between the Two Input Signals Will Reduce the Output Level or Cause Distortion For differential operation, each analog input pin of the differential pair should have a peak-to-peak voltage equal to the reference voltage, VREF, be 180 degrees out of phase with each other and be centered around VCM. 1.3.1 Single-Ended Operation Performance with a differential input signal is better than with a single-ended signal. For this reason, single-ended operation is not recommended. However, if single ended-operation is required and the resulting performance degradation is acceptable, one of the analog inputs should be connected to the d.c. mid point voltage of the driven input. The peak-topeak differential input signal at the driven input pin should be twice the reference voltage to maximize SNR and SINAD performance (Figure 2b). For example, set VREF to 1.0V, bias VIN− to 1.5V and drive VIN+ with a signal range of 0.5V to 2.5V. Because very large input signal swings can degrade distortion performance, better performance with a single-ended input can be obtained by reducing the reference voltage when maintaining a full-range output. Table 1 and Table 2 indicate the input to output relationship of the ADC14L020. TABLE 1. Input to Output Relationship – Differential Input VIN+ VCM − VREF/2 VCM − VREF/4 VCM VCM + VREF/4 VCM + VREF/2 VIN− VCM + VREF/2 VCM + VREF/4 VCM VCM − VREF/4 VCM − VREF/2 Binary Output 00 0000 0000 0000 01 0000 0000 0000 10 0000 0000 0000 11 0000 0000 0000 11 1111 1111 1111 2’s Complement Output 10 0000 0000 0000 11 0000 0000 0000 00 0000 0000 0000 01 0000 0000 0000 01 1111 1111 1111 VCM + VREF 1.3.2 Driving the Analog Inputs The VIN+ and the VIN− inputs of the ADC14L020 consist of an analog switch followed by a switched-capacitor amplifier. The capacitance seen at the analog input pins changes with the clock level, appearing as 11 pF when the clock is low, and 4.5 pF when the clock is high. As the internal sampling switch opens and closes, current pulses occur at the analog input pins, resulting in voltage spikes at the signal input pins. As a driving amplifier attempts to counteract these voltage spikes, a damped oscillation may appear at the ADC analog input. Do not attempt to filter out these pulses. Rather, use amplifiers to drive the ADC14L020 input pins that are able to react to these pulses and settle before the switch opens and another sample is taken. The LMH6702 LMH6628, LMH6622 and the LMH6655 are good amplifiers for driving the ADC14L020. To help isolate the pulses at the ADC input from the amplifier output, use RCs at the inputs, as can be seen in Figure 4 . These components should be placed close to the ADC inputs because the input pins of the ADC is the most sensitive part of the system and this is the last opportunity to filter that input. For Nyquist applications the RC pole should be at the ADC sample rate. The ADC input capacitance in the sample mode should be considered when setting the RC pole. For wideband undersampling applications, the RC pole should be set at about 1.5 to 2 times the maximum input frequency to maintain a linear delay response. A single-ended to differential conversion circuit is shown in Figure 5. Table 3 gives resistor values for that circuit to provide input signals in a range of 1.0V ± 0.5V at each of the differential input pins of the ADC14L020. TABLE 3. Resistor Values for Circuit of Figure 5 SIGNAL RANGE 0 - 0.25V 0 - 0.5V R1 open 0Ω 100Ω R2 0Ω openΩ 698Ω R3 124Ω 499Ω 100Ω R4 R5, R6 1500Ω 1000Ω 1500Ω 698Ω 499Ω 499Ω ± 0.25V TABLE 2. Input to Output Relationship – Single-Ended Input VIN+ VCM − VREF VIN− VCM Binary Output 00 0000 0000 0000 2’s Complement Output 10 0000 0000 0000 1.3.3 Input Common Mode Voltage The input common mode voltage, VCM, should be in the range of 0.5V to 2.0V and be a value such that the peak excursions of the analog signal does not go more negative than ground or more positive than 2.6V. See Section 1.2 2.0 DIGITAL INPUTS Digital TTL/CMOS compatible inputs consist of CLK, PD, and DF/DCS. 18 www.national.com ADC14L020 Applications Information 2.1 CLK (Continued) the power down mode, but can result in a reduction in SNR, SINAD and ENOB performance. 2.3 DF/DCS Duty cycle stablization and output data format are selectable using this quad state function pin. When enabled, duty cycle stabilization can compensate for clock inputs with duty cycles ranging from 20% to 80% and generate a stable internal clock, improving the performance of the part. With DF/DCS = VA the output data format is offset binary and duty cycle stabilization is applied to the clock. With DF/DCS = 0 the output data format is 2’s complement and duty cycle stabilization is applied to the clock. With DF/DCS = VRM the output data format is 2’s complement and duty cycle stabilization is not used. If DF/DCS is floating, the output data format is offset binary and duty cycle stabilization is not used. While the sense of this pin may be changed "on the fly," doing this is not recommended as the output data could be erroneous for a few clock cycles after this change is made. 3.0 OUTPUTS The ADC14L020 has 14 TTL/CMOS compatible Data Output pins. Valid data is present at these outputs while the PD pins is low. Data should be captured with the CLK signal. Depending on the setup and hold time requirements of the receiving circuit (ASIC), either the rising edge or the falling edge of the CLK signal can be used to latch the data. Generally, rising-edge capture would maximize setup time with minimal hold time; while falling-edge-capture would maximize hold time with minimal setup time. However, actual timing for the falling-edge case depends greatly on the CLK frequency and both cases also depend on the delays inside the ASIC. Refer to the tOD spec in the AC Electrical Characterisitics table. Be very careful when driving a high capacitance bus. The more capacitance the output drivers must charge for each conversion, the more instantaneous digital current flows through VDR and DR GND. These large charging current spikes can cause on-chip ground noise and couple into the analog circuitry, degrading dynamic performance. Adequate bypassing, limiting output capacitance and careful attention to the ground plane will reduce this problem. Additionally, bus capacitance beyond the specified 15 pF/pin will cause tOD to increase, making it difficult to properly latch the ADC output data. The result could be an apparent reduction in dynamic performance. To minimize noise due to output switching, minimize the load currents at the digital outputs. This can be done by connecting buffers (74ACQ541, for example) between the ADC outputs and any other circuitry. Only one driven input should be connected to each output pin. Additionally, inserting series resistors of about 33Ω at the digital outputs, close to the ADC pins, will isolate the outputs from trace and other circuit capacitances and limit the output currents, which could otherwise result in performance degradation. See Figure 4. The CLK signal controls the timing of the sampling process. Drive the clock input with a stable, low jitter clock signal in the range indicated in the Electrical Table with rise and fall times of 2 ns or less. The trace carrying the clock signal should be as short as possible and should not cross any other signal line, analog or digital, not even at 90˚. The CLK signal also drives an internal state machine. If the CLK is interrupted, or its frequency too low, the charge on internal capacitors can dissipate to the point where the accuracy of the output data will degrade. This is what limits the minimum sample rate. The clock line should be terminated at its source in the characteristic impedance of that line. Take care to maintain a constant clock line impedance throughout the length of the line. Refer to Application Note AN-905 for information on setting characteristic impedance. It is highly desirable that the the source driving the ADC CLK pin only drive that pin. However, if that source is used to drive other things, each driven pin should be a.c. terminated with a series RC to ground, as shown in Figure 4, such that the resistor value is equal to the characteristic impedance of the clock line and the capacitor value is where tPD is the signal propagation rate down the clock line, "L" is the line length and ZO is the characteristic impedance of the clock line. This termination should be as close as possible to the ADC clock pin but beyond it as seen from the clock source. Typical tPD is about 150 ps/inch (60 ps/cm) on FR-4 board material. The units of "L" and tPD should be the same (inches or centimeters). The duty cycle of the clock signal can affect the performance of the A/D Converter. Because achieving a precise duty cycle is difficult, the ADC14L020 has a Duty Cycle Stabilizer which can be enabled using the DF/DCS pin. It is designed to maintain performance over a clock duty cycle range of 20% to 80%. 2.2 PD The PD pin, when high, holds the ADC14L020 in a powerdown mode to conserve power when the converter is not being used. The power consumption in this state is 15 mW. The output data pins are undefined and the data in the pipeline is corrupted while in the power down mode. The Power Down Mode Exit Cycle time is determined by the value of the components on pins 30, 31 and 32 and is about 280 µs with the recommended components on the VRP, VRM and VRN reference bypass pins. These capacitors loose their charge in the Power Down mode and must be recharged by on-chip circuitry before conversions can be accurate. Smaller capacitor values allow slightly faster recovery from 19 www.national.com ADC14L020 Applications Information (Continued) 20157013 FIGURE 4. Application Circuit using Transformer Drive Circuit 20157014 FIGURE 5. Differential Drive Circuit of Figure 4 4.0 POWER SUPPLY CONSIDERATIONS The power supply pins should be bypassed with a 10 µF capacitor and with a 0.1 µF ceramic chip capacitor close to each power pin. Leadless chip capacitors are preferred because they have low series inductance. As is the case with all high-speed converters, the ADC14L020 is sensitive to power supply noise. Accordingly, the noise on the analog supply pin should be kept below 100 mVP-P. No pin should ever have a voltage on it that is in excess of the supply voltages, not even on a transient basis. Be especially careful of this during power turn on and turn off. The VDR pin provides power for the output drivers and may be operated from a supply in the range of 2.4V to VD. This can simplify interfacing to lower voltage devices and systems. Note, however, that tOD increases with reduced VDR. DO NOT operate the VDR pin at a voltage higher than VD. www.national.com 20 ADC14L020 Applications Information 5.0 LAYOUT AND GROUNDING (Continued) Proper grounding and proper routing of all signals are essential to ensure accurate conversion. Maintaining separate analog and digital areas of the board, with the ADC14L020 between these areas, is required to achieve specified performance. The ground return for the data outputs (DR GND) carries the ground current for the output drivers. The output current can exhibit high transients that could add noise to the conversion process. To prevent this from happening, the DR GND pins should NOT be connected to system ground in close proximity to any of the ADC14L020’s other ground pins. Capacitive coupling between the typically noisy digital circuitry and the sensitive analog circuitry can lead to poor performance. The solution is to keep the analog circuitry separated from the digital circuitry, and to keep the clock line as short as possible. Digital circuits create substantial supply and ground current transients. The logic noise thus generated could have significant impact upon system noise performance. The best logic family to use in systems with A/D converters is one which employs non-saturating transistor designs, or has low noise characteristics, such as the 74LS, 74HC(T) and 74AC(T)Q families. The worst noise generators are logic families that draw the largest supply current transients during clock or signal edges, like the 74F and the 74AC(T) families. The effects of the noise generated from the ADC output switching can be minimized through the use of 33Ω resistors in series with each data output line. Locate these resistors as close to the ADC output pins as possible. Since digital switching transients are composed largely of high frequency components, total ground plane copper weight will have little effect upon the logic-generated noise. This is because of the skin effect. Total surface area is more important than is total ground plane area. Generally, analog and digital lines should cross each other at 90˚ to avoid crosstalk. To maximize accuracy in high speed, high resolution systems, however, avoid crossing analog and digital lines altogether. It is important to keep clock lines as short as possible and isolated from ALL other lines, including other digital lines. Even the generally accepted 90˚ crossing should be avoided with the clock line as even a little coupling can cause problems at high frequencies. This is because other lines can introduce jitter into the clock line, which can lead to degradation of SNR. Also, the high speed clock can introduce noise into the analog chain. Best performance at high frequencies and at high resolution is obtained with a straight signal path. That is, the signal path through all components should form a straight line wherever possible. Be especially careful with the layout of inductors. Mutual inductance can change the characteristics of the circuit in which they are used. Inductors should not be placed side by side, even with just a small part of their bodies beside each other. The analog input should be isolated from noisy signal traces to avoid coupling of spurious signals into the input. Any external component (e.g., a filter capacitor) connected between the converter’s input pins and ground or to the reference input pin and ground should be connected to a very clean point in the ground plane. All analog circuitry (input amplifiers, filters, reference components, etc.) should be placed in the analog area of the board. All digital circuitry and I/O lines should be placed in the digital area of the board. The ADC14L020 should be between these two areas. Furthermore, all components in the reference circuitry and the input signal chain that are connected to ground should be connected together with short traces and enter the ground plane at a single, quiet point. All ground connections should have a low inductance path to ground. 6.0 DYNAMIC PERFORMANCE To achieve the best dynamic performance, the clock source driving the CLK input must be free of jitter. Isolate the ADC clock from any digital circuitry with buffers, as with the clock tree shown in Figure 6. The gates used in the clock tree must be capable of operating at frequencies much higher than those used if added jitter is to be prevented. Best performance will be obtained with a differential input drive, compared with a single-ended drive, as discussed in Sections 1.3.1 and 1.3.2. As mentioned in Section 5.0, it is good practice to keep the ADC clock line as short as possible and to keep it well away from any other signals. Other signals can introduce jitter into the clock signal, which can lead to reduced SNR performance, and the clock can introduce noise into other lines. Even lines with 90˚ crossings have capacitive coupling, so try to avoid even these 90˚ crossings of the clock line. 20157017 FIGURE 6. Isolating the ADC Clock from other Circuitry with a Clock Tree 7.0 COMMON APPLICATION PITFALLS Driving the inputs (analog or digital) beyond the power supply rails. For proper operation, all inputs should not go more than 100 mV beyond the supply rails (more than 100 mV below the ground pins or 100 mV above the supply pins). Exceeding these limits on even a transient basis may cause faulty or erratic operation. It is not uncommon for high speed digital components (e.g., 74F and 74AC devices) to exhibit overshoot or undershoot that goes above the power supply or below ground. A resistor of about 47Ω to 100Ω in series with any offending digital input, close to the signal source, will eliminate the problem. Do not allow input voltages to exceed the supply voltage, even on a transient basis. Not even during power up or power down. Be careful not to overdrive the inputs of the ADC14L020 with a device that is powered from supplies outside the range of the ADC14L020 supply. Such practice may lead to conversion inaccuracies and even to device damage. 21 www.national.com ADC14L020 Applications Information (Continued) Attempting to drive a high capacitance digital data bus. The more capacitance the output drivers must charge for each conversion, the more instantaneous digital current flows through VDR and DR GND. These large charging current spikes can couple into the analog circuitry, degrading dynamic performance. Adequate bypassing and maintaining separate analog and digital areas on the pc board will reduce this problem. Additionally, bus capacitance beyond the specified 15 pF/pin will cause tOD to increase, making it difficult to properly latch the ADC output data. The result could, again, be an apparent reduction in dynamic performance. The digital data outputs should be buffered (with 74ACQ541, for example). Dynamic performance can also be improved by adding series resistors at each digital output, close to the ADC14L020, which reduces the energy coupled back into the converter output pins by limiting the output current. A reasonable value for these resistors is 33Ω. Using an inadequate amplifier to drive the analog input. As explained in Section 1.3, the capacitance seen at the input alternates between 11 pF and 4.5 pF, depending upon the phase of the clock. This dynamic load is more difficult to drive than is a fixed capacitance. If the amplifier exhibits overshoot, ringing, or any evidence of instability, even at a very low level, it will degrade performance. A small series resistor at each amplifier output and a capacitor at the analog inputs (as shown in Figure 5) will improve performance. The LMH6702 and the LMH6628 have been successfully used to drive the analog inputs of the ADC14L020. Also, it is important that the signals at the two inputs have exactly the same amplitude and be exactly 180o out of phase with each other. Board layout, especially equality of the length of the two traces to the input pins, will affect the effective phase between these two signals. Remember that an operational amplifier operated in the non-inverting configuration will exhibit more time delay than will the same device operating in the inverting configuration. Operating with the reference pins outside of the specified range. As mentioned in Section 1.2, when using an external reference, VREF should be in the range of 0.8V ≤ VREF ≤ 1.2V Operating outside of these limits could lead to performance degradation. Inadequate network on Reference Bypass pins (VRP, VRN, and VRM). As mentioned in Section 1.2, these pins should be bypassed with 0.1 µF capacitors to ground, and 10 µF capacitor should be connected between pins VRP and VRN. Using a clock source with excessive jitter, using excessively long clock signal trace, or having other signals coupled to the clock signal trace. This will cause the sampling interval to vary, causing excessive output noise and a reduction in SNR and SINAD performance. www.national.com 22 ADC14L020 14-Bit, 20 MSPS, 150 mW A/D Converter Physical Dimensions inches (millimeters) unless otherwise noted 32-Lead LQFP Package Ordering Number ADC14L020CIVY NS Package Number VBE32A National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. For the most current product information visit us at www.national.com. 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