LTC2298CUP#PBF

LTC2298/LTC2297/LTC2296 Dual 14-Bit, 65/40/25Msps Low Power 3V ADCs DESCRIPTIO U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ The LTC®2298/LTC2297/LTC2296 are 14-bit 65Msps/ 40Msps/25Msps, low power dual 3V A/D converters designed for digitizing high frequency, wide dynamic range signals. The LTC2298/LTC2297/LTC2296 are perfect for demanding imaging and communications applications with AC performance that includes 74.3dB SNR and 90dB SFDR for signals at the Nyquist frequency. Integrated Dual 14-Bit ADCs Sample Rate: 65Msps/40Msps/25Msps Single 3V Supply (2.7V to 3.4V) Low Power: 400mW/235mW/150mW 74.3dB SNR 90dB SFDR 110dB Channel Isolation at 100MHz Multiplexed or Separate Data Bus Flexible Input: 1VP-P to 2VP-P Range 575MHz Full Power Bandwidth S/H Clock Duty Cycle Stabilizer Shutdown and Nap Modes Pin Compatible Family 105Msps: LTC2282 (12-Bit), LTC2284 (14-Bit) 80Msps: LTC2294 (12-Bit), LTC2299 (14-Bit) 65Msps: LTC2293 (12-Bit), LTC2298 (14-Bit) 40Msps: LTC2292 (12-Bit), LTC2297 (14-Bit) 25Msps: LTC2291 (12-Bit), LTC2296 (14-Bit) 10Msps: LTC2290 (12-Bit), LTC2295 (14-Bit) 64-Pin (9mm × 9mm) QFN Package DC specs include ±1.2LSB INL (typ), ±0.5LSB DNL (typ) and no missing codes over temperature. The transition noise is a low 1LSBRMS. A single 3V supply allows low power operation. A separate output supply allows the outputs to drive 0.5V to 3.6V logic. An optional multiplexer allows both channels to share a digital output bus. A single-ended CLK input controls converter operation. An optional clock duty cycle stabilizer allows high performance at full speed for a wide range of clock duty cycles. , LTC and LT are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. U APPLICATIO S ■ ■ ■ ■ Wireless and Wired Broadband Communication Imaging Systems Spectral Analysis Portable Instrumentation U TYPICAL APPLICATIO + ANALOG INPUT A INPUT S/H – LTC2298: SNR vs Input Frequency, –1dB, 2V Range, 65Msps OVDD 14-BIT PIPELINED ADC CORE OUTPUT DRIVERS 75 D13A •• • D0A 74 CLK A CLOCK/DUTY CYCLE CONTROL CLK B CLOCK/DUTY CYCLE CONTROL MUX SNR (dBFS) OGND 73 72 71 OVDD + ANALOG INPUT B INPUT S/H – 14-BIT PIPELINED ADC CORE OUTPUT DRIVERS D13B •• • D0B 70 0 100 50 150 INPUT FREQUENCY (MHz) 200 229876 TA01b OGND 229876 TA01 229876fa 1 LTC2298/LTC2297/LTC2296 W W U W ABSOLUTE AXI U RATI GS OVDD = VDD (Notes 1, 2) Supply Voltage (VDD) ................................................. 4V Digital Output Ground Voltage (OGND) ....... –0.3V to 1V Analog Input Voltage (Note 3) ..... –0.3V to (VDD + 0.3V) Digital Input Voltage .................... –0.3V to (VDD + 0.3V) Digital Output Voltage ................ –0.3V to (OVDD + 0.3V) Power Dissipation ............................................ 1500mW Operating Temperature Range LTC2298C, LTC2297C, LTC2296C ........... 0°C to 70°C LTC2298I, LTC2297I, LTC2296I ..........–40°C to 85°C Storage Temperature Range ..................–65°C to 125°C U W U PACKAGE/ORDER I FOR ATIO 64 GND 63 VDD 62 SENSEA 61 VCMA 60 MODE 59 SHDNA 58 OEA 57 OFA 56 DA13 55 DA12 54 DA11 53 DA10 52 DA9 51 DA8 50 OGND 49 OVDD TOP VIEW AINA+ 1 AINA– 2 REFHA 3 REFHA 4 REFLA 5 REFLA 6 VDD 7 CLKA 8 CLKB 9 VDD 10 REFLB 11 REFLB 12 REFHB 13 REFHB 14 AINB– 15 AINB+ 16 GND 17 VDD 18 SENSEB 19 VCMB 20 MUX 21 SHDNB 22 OEB 23 DB0 24 DB1 25 DB2 26 DB3 27 DB4 28 DB5 29 DB6 30 OGND 31 OVDD 32 65 48 DA7 47 DA6 46 DA5 45 DA4 44 DA3 43 DA2 42 DA1 41 DA0 40 OFB 39 DB13 38 DB12 37 DB11 36 DB10 35 DB9 34 DB8 33 DB7 ORDER PART NUMBER QFN PART* MARKING LTC2298CUP LTC2298IUP LTC2297CUP LTC2297IUP LTC2296CUP LTC2296IUP LTC2298UP LTC2297UP LTC2296UP Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ UP PACKAGE 64-LEAD (9mm × 9mm) PLASTIC QFN TJMAX = 125°C, θJA = 20°C/W EXPOSED PAD (PIN 65) IS GND AND MUST BE SOLDERED TO PCB Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. U CO VERTER CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 4) PARAMETER Resolution (No Missing Codes) Integral Linearity Error Differential Linearity Error Offset Error Gain Error Offset Drift Full-Scale Drift Gain Matching Offset Matching Transition Noise CONDITIONS ● Differential Analog Input (Note 5) Differential Analog Input ● (Note 6) External Reference ● Internal Reference External Reference SENSE = 1V ● ● MIN 14 LTC2298 TYP MAX MIN 14 LTC2297 TYP MAX MIN 14 LTC2296 TYP MAX –5 –1 ±1.2 ±0.5 5 1 –5 –1 ±1.2 ±0.5 5 1 –5 –1 ±1.2 ±0.5 5 1 –12 –2.5 ±2 ±0.5 ±10 ±30 ±5 ±0.3 ±2 1 12 2.5 –12 –2.5 ±2 ±0.5 ±10 ±30 ±5 ±0.3 ±2 1 12 2.5 –12 –2.5 ±2 ±0.5 ±10 ±30 ±5 ±0.3 ±2 1 12 2.5 UNITS Bits LSB LSB mV %FS µV/°C ppm/°C ppm/°C %FS mV LSBRMS 229876fa 2 LTC2298/LTC2297/LTC2296 U U A ALOG I PUT The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 4) SYMBOL PARAMETER VIN Analog Input Range (AIN+ –AIN–) CONDITIONS VIN,CM Analog Input Common Mode (AIN+ +AIN –)/2 MIN 2.7V < VDD < 3.4V (Note 7) ● TYP MAX UNITS ±0.5V to ±1V V Differential Input (Note 7) ● 1 1.5 1.9 V Single Ended Input (Note 7) ● 0.5 1.5 2 V 0V < AIN+, AIN– ● –1 1 µA IIN Analog Input Leakage Current < VDD ISENSE SENSEA, SENSEB Input Leakage 0V < SENSEA, SENSEB < 1V ● –3 3 µA IMODE MODE Input Leakage Current 0V < MODE < VDD ● –3 3 µA tAP Sample-and-Hold Acquisition Delay Time 0 ns tJITTER Sample-and-Hold Acquisition Delay Time Jitter 0.2 psRMS CMRR Analog Input Common Mode Rejection Ratio 80 dB 575 MHz Full Power Bandwidth Figure 8 Test Circuit W U DY A IC ACCURACY The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. AIN = –1dBFS. (Note 4) SYMBOL PARAMETER CONDITIONS SNR Signal-to-Noise Ratio 5MHz Input SFDR Spurious Free Dynamic Range 2nd or 3rd Harmonic MIN Spurious Free Dynamic Range 4th Harmonic or Higher 12.5MHz Input ● 20MHz Input ● 30MHz Input ● IMD MIN 74.4 72.4 72.1 LTC2296 TYP MAX UNITS 74.5 dB 74.2 dB 74.4 dB 74.3 dB 70MHz Input 74.3 73.9 140MHz Input 73.9 73.3 73 dB 90 90 90 dB 90 dB 5MHz Input 12.5MHz Input ● 20MHz Input ● 30MHz Input ● 73.4 76 75 75 90 dB dB 90 dB 85 85 85 dB 140MHz Input 80 80 80 dB 5MHz Input 90 90 90 dB 90 dB 12.5MHz Input ● 20MHz Input ● 30MHz Input ● 80 80 78 5MHz Input 12.5MHz Input ● 20MHz Input ● 30MHz Input ● 90 dB 90 dB 90 140MHz Input Signal-to-Noise Plus Distortion Ratio LTC2297 TYP MAX 72.7 70MHz Input S/(N+D) MIN 74.3 70MHz Input SFDR LTC2298 TYP MAX 90 90 90 90 90 dB 74.3 74.4 74.5 dB 74.2 dB 72.2 71.9 71.6 dB 74.3 dB 74.2 dB 70MHz Input 74.1 73.6 73.4 140MHz Input 71.9 71.9 71.8 dB 90 90 90 dB –110 –110 –110 Intermodulation Distortion fIN = Nyquist, Nyquist + 1MHz Crosstalk fIN = Nyquist dB dB 229876fa 3 LTC2298/LTC2297/LTC2296 U U U I TER AL REFERE CE CHARACTERISTICS (Note 4) PARAMETER CONDITIONS MIN TYP MAX UNITS VCM Output Voltage IOUT = 0 1.475 1.500 1.525 V ±25 VCM Output Tempco ppm/°C VCM Line Regulation 2.7V < VDD < 3.3V 3 mV/V VCM Output Resistance –1mA < IOUT < 1mA 4 Ω U U DIGITAL I PUTS A D DIGITAL OUTPUTS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 4) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS LOGIC INPUTS (CLK, OE, SHDN, MUX) VIH High Level Input Voltage VDD = 3V ● VIL Low Level Input Voltage VDD = 3V ● IIN Input Current VIN = 0V to VDD ● CIN Input Capacitance (Note 7) 2 V –10 0.8 V 10 µA 3 pF LOGIC OUTPUTS OVDD = 3V COZ Hi-Z Output Capacitance OE = High (Note 7) 3 pF ISOURCE Output Source Current VOUT = 0V 50 mA ISINK Output Sink Current VOUT = 3V 50 mA VOH High Level Output Voltage IO = –10µA IO = –200µA ● IO = 10µA IO = 1.6mA ● VOL Low Level Output Voltage 2.7 2.995 2.99 0.005 0.09 V V 0.4 V V OVDD = 2.5V VOH High Level Output Voltage IO = –200µA 2.49 V VOL Low Level Output Voltage IO = 1.6mA 0.09 V VOH High Level Output Voltage IO = –200µA 1.79 V VOL Low Level Output Voltage IO = 1.6mA 0.09 V OVDD = 1.8V 229876fa 4 LTC2298/LTC2297/LTC2296 U W POWER REQUIRE E TS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 8) MIN LTC2298 TYP MAX MIN LTC2297 TYP MAX MIN LTC2296 TYP MAX SYMBOL PARAMETER CONDITIONS UNITS VDD Analog Supply Voltage (Note 9) ● 2.7 3 3.4 2.7 3 3.4 2.7 3 3.4 V OVDD Output Supply Voltage (Note 9) ● 0.5 3 3.6 0.5 3 3.6 0.5 3 3.6 V IVDD Supply Current Both ADCs at fS(MAX) ● 133 150 78 95 50 60 mA PDISS Power Dissipation Both ADCs at fS(MAX) ● 400 450 235 285 150 180 mW PSHDN Shutdown Power (Each Channel) SHDN = H, OE = H, No CLK 2 2 2 mW PNAP Nap Mode Power (Each Channel) SHDN = H, OE = L, No CLK 15 15 15 mW WU TI I G CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 4) CONDITIONS MIN LTC2298 TYP MAX MIN LTC2297 TYP MAX PARAMETER fs Sampling Frequency (Note 9) ● 1 65 1 40 1 25 MHz tL CLK Low Time Duty Cycle Stabilizer Off Duty Cycle Stabilizer On (Note 7) ● ● 7.3 5 7.7 7.7 500 500 11.8 5 12.5 12.5 500 500 18.9 5 20 20 500 500 ns ns tH CLK High Time Duty Cycle Stabilizer Off Duty Cycle Stabilizer On (Note 7) ● ● 7.3 5 7.7 7.7 500 500 11.8 5 12.5 12.5 500 500 18.9 5 20 20 500 500 ns ns tAP Sample-and-Hold Aperture Delay tD CLK to DATA Delay CL = 5pF (Note 7) ● 1.4 2.7 5.4 1.4 2.7 5.4 1.4 2.7 5.4 ns tMD MUX to DATA Delay CL = 5pF (Note 7) ● 1.4 2.7 5.4 1.4 2.7 5.4 1.4 2.7 5.4 ns Data Access Time After OE↓ ● 4.3 10 4.3 10 4.3 10 ns ● 3.3 8.5 3.3 8.5 3.3 8.5 0 CL = 5pF (Note 7) BUS Relinquish Time (Note 7) Pipeline Latency Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: All voltage values are with respect to ground with GND and OGND wired together (unless otherwise noted). Note 3: When these pin voltages are taken below GND or above VDD, they will be clamped by internal diodes. This product can handle input currents of greater than 100mA below GND or above VDD without latchup. Note 4: VDD = 3V, fSAMPLE = 65MHz (LTC2298), 40MHz (LTC2297), or 25MHz (LTC2296), input range = 2VP-P with differential drive, unless otherwise noted. 5 MIN LTC2296 TYP MAX SYMBOL 0 5 0 5 UNITS ns ns Cycles Note 5: Integral nonlinearity is defined as the deviation of a code from a straight line passing through the actual endpoints of the transfer curve. The deviation is measured from the center of the quantization band. Note 6: Offset error is the offset voltage measured from –0.5 LSB when the output code flickers between 00 0000 0000 0000 and 11 1111 1111 1111. Note 7: Guaranteed by design, not subject to test. Note 8: VDD = 3V, fSAMPLE = 65MHz (LTC2298), 40MHz (LTC2297), or 25MHz (LTC2296), input range = 1VP-P with differential drive. The supply current and power dissipation are the sum total for both channels with both channels active. Note 9: Recommended operating conditions. 229876fa 5 LTC2298/LTC2297/LTC2296 U W TYPICAL PERFOR A CE CHARACTERISTICS LTC2298: Typical INL, 2V Range, 65Msps LTC2298/LTC2297/LTC2296: Crosstalk vs Input Frequency INL ERROR (LSB) CROSSTALK (dB) –105 –110 –115 –120 –125 –130 2.0 1.00 1.5 0.75 1.0 0.50 DNL ERROR (LSB) –100 LTC2298: Typical DNL, 2V Range, 65Msps 0.5 0 –0.5 20 –0.25 –0.50 –1.5 –0.75 100 40 60 80 INPUT FREQUENCY (MHz) 0 –1.0 –2.0 0 0.25 –1.00 0 4096 8192 CODE 12288 0 16384 4096 8192 CODE 2298 G01 12288 16384 2298 G02 229876 G01 0 –10 –20 –20 –20 –30 –30 –30 –40 –50 –60 –70 –80 AMPLITUDE (dB) 0 –10 AMPLITUDE (dB) –40 –50 –60 –70 –80 –40 –50 –60 –70 –80 –90 –90 –90 –100 –100 –100 –110 –110 –110 –120 –120 0 5 10 15 20 25 FREQUENCY (MHz) 30 –20 –20 –30 –30 AMPLITUDE (dB) 0 –10 –40 –50 –60 –70 –80 10 15 20 25 FREQUENCY (MHz) 30 2298 G05 LTC2298: Grounded Input Histogram, 65Msps 21824 20412 20000 –70 15000 10224 10000 9042 –80 –90 –110 –110 2298 G06 5 25000 –60 –100 30 0 2298 G04 –50 –90 10 15 20 25 FREQUENCY (MHz) –120 30 –40 –100 5 10 15 20 25 FREQUENCY (MHz) LTC2298: 8192 Point 2-Tone FFT, fIN = 28.2MHz and 26.8MHz, –1dB, 2V Range, 65Msps 0 0 5 2298 G03 –10 –120 0 COUNT AMPLITUDE (dB) 0 –10 LTC2298: 8192 Point FFT, fIN = 140MHz, –1dB, 2V Range, 65Msps AMPLITUDE (dB) LTC2298: 8192 Point FFT, fIN = 70MHz, –1dB, 2V Range, 65Msps LTC2298: 8192 Point FFT, fIN = 30MHz, –1dB, 2V Range, 65Msps LTC2298: 8192 Point FFT, fIN = 5MHz, –1dB, 2V Range, 65Msps –120 5000 2116 172 0 5 10 15 20 25 FREQUENCY (MHz) 30 2298 G06a 0 1596 121 8196 8197 8198 8199 8200 8201 8202 8203 CODE 2298 G08 229876fa 6 LTC2298/LTC2297/LTC2296 U W TYPICAL PERFOR A CE CHARACTERISTICS LTC2298: SNR vs Input Frequency, –1dB, 2V Range, 65Msps LTC2298: SNR and SFDR vs Sample Rate, 2V Range, fIN = 5MHz, –1dB LTC2298: SFDR vs Input Frequency, –1dB, 2V Range, 65Msps 100 75 110 95 100 SNR AND SFDR (dBFS) 74 SFDR (dBFS) SNR (dBFS) 90 73 72 85 80 75 90 80 70 71 70 70 65 100 50 150 INPUT FREQUENCY (MHz) 0 60 200 80 SFDR: DCS ON LTC2298: SFDR vs Input Level, fIN = 30MHz, 2V Range, 65Msps 120 dBFS 110 70 SFDR: DCS OFF 85 80 60 SFDR (dBc AND dBFS) SNR (dBc AND dBFS) 100 90 50 dBc 40 30 20 75 SNR: DCS ON 40 45 50 55 60 CLOCK DUTY CYCLE (%) 65 0 –60 70 2298 G12 –50 –40 –30 –20 INPUT LEVEL (dBFS) –10 0 2298 G13 80 dBc 70 90dBc SFDR REFERENCE LINE 60 50 20 –60 –50 –40 –30 –20 INPUT LEVEL (dBFS) –10 0 2298 G14 LTC2298: IOVDD vs Sample Rate, 5MHz Sine Wave Input, –1dB, OVDD = 1.8V LTC2298: IVDD vs Sample Rate, 5MHz Sine Wave Input, –1dB 155 12 145 10 135 8 1V RANGE 125 2V RANGE 6 115 4 105 2 95 90 30 IOVDD (mA) 35 IVDD (mA) 30 dBFS 40 10 SNR: DCS OFF 70 0 10 20 30 40 50 60 70 80 90 100 110 SAMPLE RATE (Msps) 2298 G11 2298 G10 LTC2298: SNR vs Input Level, fIN = 30MHz, 2V Range, 65Msps 95 SNR AND SFDR (dBFS) 100 150 INPUT FREQUENCY (MHz) 2298 G09 LTC2298: SNR and SFDR vs Clock Duty Cycle, 65Msps 100 50 0 200 0 10 20 30 40 50 60 SAMPLE RATE (Msps) 70 80 2298 G15 0 0 10 20 30 40 50 60 SAMPLE RATE (Msps) 70 80 2298 G16 229876fa 7 LTC2298/LTC2297/LTC2296 U W TYPICAL PERFOR A CE CHARACTERISTICS LTC2297: Typical INL, 2V Range, 40Msps 0 1.00 0.75 1.0 0.50 0.5 0 –0.5 –1.0 –10 –20 –30 AMPLITUDE (dB) 1.5 DNL ERROR (LSB) 0.25 0 –0.25 –1.5 –0.75 –2.0 –1.00 0 4096 8192 CODE 12288 16384 –50 –60 –70 –80 –100 –110 –120 4096 0 8192 CODE 2297 G01 12288 16384 0 0 –10 –10 –20 –20 –20 –30 –30 –30 AMPLITUDE (dB) 0 –50 –60 –70 –80 –40 –50 –60 –70 –80 –70 –80 –90 –100 –100 –110 –110 –110 –120 –120 20 –120 0 5 2297 G04 LTC2297: 8192 Point 2-Tone FFT, fIN = 21.6MHz and 23.6MHz, –1dB, 2V Range, 40Msps 10 15 FREQUENCY (MHz) 0 20 2297 G05 LTC2297: Grounded Input Histogram, 40Msps 0 10 15 FREQUENCY (MHz) 20 2297 G06 75 24558 25000 74 –30 –40 5 LTC2297: SNR vs Input Frequency, –1dB, 2V Range, 40Msps 30000 –10 –20 2297 G03 –60 –100 10 15 FREQUENCY (MHz) 20 –50 –90 5 10 15 FREQUENCY (MHz) –40 –90 0 5 LTC2297: 8192 Point FFT, fIN = 140MHz, –1dB, 2V Range, 40Msps –10 –40 0 2297 G02 LTC2297: 8192 Point FFT, fIN = 70MHz, –1dB, 2V Range, 40Msps LTC2297: 8192 Point FFT, fIN = 30MHz, –1dB, 2V Range, 40Msps –60 –70 –80 14833 15000 SNR (dBFS) 20000 –50 COUNT AMPLITUDE (dB) –40 –90 –0.50 AMPLITUDE (dB) INL ERROR (LSB) 2.0 AMPLITUDE (dB) LTC2297: 8192 Point FFT, fIN = 5MHz, –1dB, 2V Range, 40Msps LTC2297: Typical DNL, 2V Range, 40Msps 15714 73 72 10000 –90 –100 4641 5000 –110 –120 0 5 10 15 FREQUENCY (MHz) 20 2297 G07 0 30 640 71 4520 546 36 8184 8185 8186 818781888189 8190 81918192 CODE 2297 G08 70 0 100 50 150 INPUT FREQUENCY (MHz) 200 2297 G09 229876fa 8 LTC2298/LTC2297/LTC2296 U W TYPICAL PERFOR A CE CHARACTERISTICS LTC2297: SNR and SFDR vs Sample Rate, 2V Range, fIN = 5MHz, –1dB LTC2297: SFDR vs Input Frequency, –1dB, 2V Range, 40Msps 110 80 95 SFDR SNR AND SFDR (dBFS) 100 90 85 80 75 dBFS 70 SNR (dBc AND dBFS) 100 SFDR (dBFS) LTC2297: SNR vs Input Level, fIN = 5MHz, 2V Range, 40Msps 90 80 SNR 60 50 dBc 40 30 20 70 70 10 65 60 50 100 0 200 150 INPUT FREQUENCY (MHz) 0 40 20 60 SAMPLE RATE (Msps) 0 –60 80 –50 –40 –30 –20 INPUT LEVEL (dBFS) –10 2297 G12 2297 G11 2297 G10 LTC2297: IOVDD vs Sample Rate, 5MHz Sine Wave Input, –1dB, OVDD = 1.8V LTC2297: IVDD vs Sample Rate, 5MHz Sine Wave Input, –1dB LTC2297: SFDR vs Input Level, fIN = 5MHz, 2V Range, 40Msps 120 0 100 8 90 6 110 80 IVDD (mA) SNR (dBc AND dBFS) 90 dBc 70 90dBc SFDR REFERENCE LINE 60 IOVDD (mA) dBFS 100 2V RANGE 80 4 1V RANGE 50 2 70 40 30 20 –60 – 50 – 40 –30 –20 INPUT LEVEL (dBFS) –10 60 0 0 10 30 40 20 SAMPLE RATE (Msps) LTC2296: Typical INL, 2V Range, 25Msps 1.0 0.50 0 –20 –30 0.25 0 –0.25 –0.50 –1.0 –1.5 –0.75 –2.0 –1.00 0 4096 8192 CODE 12288 16384 2296 G01 50 –10 AMPLITUDE (dB) 0.75 DNL ERROR (LSB) 1.5 –0.5 30 40 20 SAMPLE RATE (Msps) LTC2296: 8192 Point FFT, fIN = 5MHz, –1dB, 2V Range, 25Msps 1.00 2.0 0 10 2297 G15 LTC2296: Typical DNL, 2V Range, 25Msps 0.5 0 2297 G14 2297 G13 INL ERROR (LSB) 0 50 –40 –50 –60 –70 –80 –90 –100 –110 –120 0 4096 8192 CODE 12288 16384 2296 G02 0 2 4 6 8 10 FREQUENCY (MHz) 12 2296 G03 229876fa 9 LTC2298/LTC2297/LTC2296 U W TYPICAL PERFOR A CE CHARACTERISTICS 0 –10 –20 –20 –20 –30 –30 –30 –40 –50 –60 –70 –80 AMPLITUDE (dB) 0 –10 AMPLITUDE (dB) AMPLITUDE (dB) 0 –10 –40 –50 –60 –70 –80 –40 –50 –60 –70 –80 –90 –90 –90 –100 –100 –100 –110 –110 –110 –120 –120 0 2 4 6 8 10 FREQUENCY (MHz) 12 0 2 4 6 8 10 FREQUENCY (MHz) –120 12 0 2 12 4 6 8 10 FREQUENCY (MHz) 2296 G05 2296 G04 LTC2296: 8192 Point 2-Tone FFT, fIN = 10.9MHz and 13.8MHz, –1dB, 2V Range, 25Msps 2296 G06 LTC2296: Grounded Input Histogram, 25Msps LTC2296: SNR vs Input Frequency, –1dB, 2V Range, 25Msps 25000 0 75 22016 –10 –20 20000 74 18803 –30 –50 –60 –70 15000 SNR (dBFS) –40 COUNT AMPLITUDE (dB) LTC2296: 8192 Point FFT, fIN = 140MHz, –1dB, 2V Range, 25Msps LTC2296: 8192 Point FFT, fIN = 70MHz, –1dB, 2V Range, 25Msps LTC2296: 8192 Point FFT, fIN = 30MHz, –1dB, 2V Range, 25Msps 13373 10000 –80 73 72 6919 –90 5000 –100 –110 –120 0 2 4 6 8 10 FREQUENCY (MHz) 0 12 2296 G07 71 3227 43 853 278 70 8179 8180 8181 8182 8183 8184 8185 8186 CODE 2296 G08 LTC2296: SNR and SFDR vs Sample Rate, 2V Range, fIN = 5MHz, –1dB LTC2296: SFDR vs Input Frequency, –1dB, 2V Range, 25Msps 100 80 110 dBFS 70 85 80 75 SNR (dBc AND dBFS) SNR AND SFDR (dBFS) 100 90 200 2296 G09 LTC2296: SNR vs Input Level, fIN = 5MHz, 2V Range, 25Msps 95 SFDR (dBFS) 100 50 150 INPUT FREQUENCY (MHz) 0 SFDR 90 80 SNR 60 50 dBc 40 30 20 70 70 10 65 0 50 100 150 INPUT FREQUENCY (MHz) 200 2296 G10 60 0 10 20 30 40 SAMPLE RATE (Msps) 50 2296 G11 0 –60 –50 –30 –40 –20 INPUT LEVEL (dBFS) –10 0 2296 G12 229876fa 10 LTC2298/LTC2297/LTC2296 U W TYPICAL PERFOR A CE CHARACTERISTICS LTC2296: IOVDD vs Sample Rate, 5MHz Sine Wave Input, –1dB, OVDD = 1.8V LTC2296: IVDD vs Sample Rate, 5MHz Sine Wave Input, –1dB LTC2296: SFDR vs Input Level, fIN = 5MHz, 2V Range, 25Msps 70 120 6 110 dBFS 60 90 dBc 70 90dBc SFDR REFERENCE LINE 60 IOVDD (mA) 4 80 IVDD (mA) SFDR (dBc AND dBFS) 100 2V RANGE 50 1V RANGE 2 50 40 40 30 30 –50 –40 –30 –20 INPUT LEVEL (dBFS) –10 0 2296 G13 0 5 25 20 15 10 SAMPLE RATE (Msps) 30 35 2296 G14 0 0 5 25 20 15 10 SAMPLE RATE (Msps) 30 35 2296 G15 U U 20 –60 U PI FU CTIO S AINA+ (Pin 1): Channel A Positive Differential Analog Input. AINA– (Pin 2): Channel A Negative Differential Analog Input. REFHA (Pins 3, 4): Channel A High Reference. Short together and bypass to Pins 5, 6 with a 0.1µF ceramic chip capacitor as close to the pin as possible. Also bypass to Pins 5, 6 with an additional 2.2µF ceramic chip capacitor and to ground with a 1µF ceramic chip capacitor. REFLA (Pins 5, 6): Channel A Low Reference. Short together and bypass to Pins 3, 4 with a 0.1µF ceramic chip capacitor as close to the pin as possible. Also bypass to Pins 3, 4 with an additional 2.2µF ceramic chip capacitor and to ground with a 1µF ceramic chip capacitor. VDD (Pins 7, 10, 18, 63): Analog 3V Supply. Bypass to GND with 0.1µF ceramic chip capacitors. CLKA (Pin 8): Channel A Clock Input. The input sample starts on the positive edge. CLKB (Pin 9): Channel B Clock Input. The input sample starts on the positive edge. REFLB (Pins 11, 12): Channel B Low Reference. Short together and bypass to Pins 13, 14 with a 0.1µF ceramic chip capacitor as close to the pin as possible. Also bypass to Pins 13, 14 with an additional 2.2µF ceramic chip capacitor and to ground with a 1µF ceramic chip capacitor. REFHB (Pins 13, 14): Channel B High Reference. Short together and bypass to Pins 11, 12 with a 0.1µF ceramic chip capacitor as close to the pin as possible. Also bypass to Pins 11, 12 with an additional 2.2µF ceramic chip capacitor and to ground with a 1µF ceramic chip capacitor. AINB– (Pin 15): Channel B Negative Differential Analog Input. AINB+ (Pin 16): Channel B Positive Differential Analog Input. GND (Pins 17, 64): ADC Power Ground. SENSEB (Pin 19): Channel B Reference Programming Pin. Connecting SENSEB to VCMB selects the internal reference and a ±0.5V input range. VDD selects the internal reference and a ±1V input range. An external reference greater than 0.5V and less than 1V applied to SENSEB selects an input range of ±VSENSEB. ±1V is the largest valid input range. VCMB (Pin 20): Channel B 1.5V Output and Input Common Mode Bias. Bypass to ground with 2.2µF ceramic chip capacitor. Do not connect to VCMA. 229876fa 11 LTC2298/LTC2297/LTC2296 U U U PI FU CTIO S MUX (Pin 21): Digital Output Multiplexer Control. If MUX is High, Channel A comes out on DA0-DA13, OFA; Channel B comes out on DB0-DB13, OFB. If MUX is Low, the output busses are swapped and Channel A comes out on DB0DB13, OFB; Channel B comes out on DA0-DA13, OFA. To multiplex both channels onto a single output bus, connect MUX, CLKA and CLKB together. SHDNB (Pin 22): Channel B Shutdown Mode Selection Pin. Connecting SHDNB to GND and OEB to GND results in normal operation with the outputs enabled. Connecting SHDNB to GND and OEB to VDD results in normal operation with the outputs at high impedance. Connecting SHDNB to VDD and OEB to GND results in nap mode with the outputs at high impedance. Connecting SHDNB to VDD and OEB to VDD results in sleep mode with the outputs at high impedance. OEB (Pin 23): Channel B Output Enable Pin. Refer to SHDNB pin function. DB0 – DB13 (Pins 24 to 30, 33 to 39): Channel B Digital Outputs. DB13 is the MSB. OGND (Pins 31, 50): Output Driver Ground. OVDD (Pins 32, 49): Positive Supply for the Output Drivers. Bypass to ground with 0.1µF ceramic chip capacitor. OFB (Pin 40): Channel B Overflow/Underflow Output. High when an overflow or underflow has occurred. DA0 – DA13 (Pins 41 to 48, 51 to 56): Channel A Digital Outputs. DA13 is the MSB. OFA (Pin 57): Channel A Overflow/Underflow Output. High when an overflow or underflow has occurred. SHDNA (Pin 59): Channel A Shutdown Mode Selection Pin. Connecting SHDNA to GND and OEA to GND results in normal operation with the outputs enabled. Connecting SHDNA to GND and OEA to VDD results in normal operation with the outputs at high impedance. Connecting SHDNA to VDD and OEA to GND results in nap mode with the outputs at high impedance. Connecting SHDNA to VDD and OEA to VDD results in sleep mode with the outputs at high impedance. MODE (Pin 60): Output Format and Clock Duty Cycle Stabilizer Selection Pin. Note that MODE controls both channels. Connecting MODE to GND selects offset binary output format and turns the clock duty cycle stabilizer off. 1/3 VDD selects offset binary output format and turns the clock duty cycle stabilizer on. 2/3 VDD selects 2’s complement output format and turns the clock duty cycle stabilizer on. VDD selects 2’s complement output format and turns the clock duty cycle stabilizer off. VCMA (Pin 61): Channel A 1.5V Output and Input Common Mode Bias. Bypass to ground with 2.2µF ceramic chip capacitor. Do not connect to VCMB. SENSEA (Pin 62): Channel A Reference Programming Pin. Connecting SENSEA to VCMA selects the internal reference and a ±0.5V input range. VDD selects the internal reference and a ±1V input range. An external reference greater than 0.5V and less than 1V applied to SENSEA selects an input range of ±VSENSEA. ±1V is the largest valid input range. GND (Exposed Pad) (Pin 65): ADC Power Ground. The Exposed Pad on the bottom of the package needs to be soldered to ground. OEA (Pin 58): Channel A Output Enable Pin. Refer to SHDNA pin function. 229876fa 12 LTC2298/LTC2297/LTC2296 W FUNCTIONAL BLOCK DIAGRA U U AIN+ AIN– VCM INPUT S/H FIRST PIPELINED ADC STAGE SECOND PIPELINED ADC STAGE THIRD PIPELINED ADC STAGE FOURTH PIPELINED ADC STAGE FIFTH PIPELINED ADC STAGE 1.5V REFERENCE SIXTH PIPELINED ADC STAGE SHIFT REGISTER AND CORRECTION 2.2µF RANGE SELECT REFH SENSE REFL INTERNAL CLOCK SIGNALS OVDD REF BUF OF D13 CLOCK/DUTY CYCLE CONTROL DIFF REF AMP CONTROL LOGIC OUTPUT DRIVERS • • • D0 REFH 0.1µF 229876 F01 REFL OGND CLK MODE SHDN OE 2.2µF 1µF 1µF Figure 1. Functional Block Diagram (Only One Channel is Shown) 229876fa 13 LTC2298/LTC2297/LTC2296 W UW TI I G DIAGRA S Dual Digital Output Bus Timing (Only One Channel is Shown) tAP N+4 N+2 N ANALOG INPUT N+1 tH N+3 N+5 tL CLK tD N–4 N–5 D0-D13, OF N–3 N–2 N–1 N 229876 TD01 Multiplexed Digital Output Bus Timing tAPA ANALOG INPUT A A+4 A+2 A A+1 A+3 tAPB ANALOG INPUT B B+4 B+2 B B+1 tH tL A–5 B–5 B+3 CLKA = CLKB = MUX D0A-D13A, OFA A–4 tD D0B-D13B, OFB B–5 B–4 A–3 B–3 A–2 B–2 B–3 A–3 B–2 A–2 A–1 t MD A–5 B–4 A–4 B–1 229876 TD02 229876fa 14 LTC2298/LTC2297/LTC2296 U W U U APPLICATIO S I FOR ATIO DYNAMIC PERFORMANCE Signal-to-Noise Plus Distortion Ratio The signal-to-noise plus distortion ratio [S/(N + D)] is the ratio between the RMS amplitude of the fundamental input frequency and the RMS amplitude of all other frequency components at the ADC output. The output is band limited to frequencies above DC to below half the sampling frequency. Signal-to-Noise Ratio The signal-to-noise ratio (SNR) is the ratio between the RMS amplitude of the fundamental input frequency and the RMS amplitude of all other frequency components except the first five harmonics and DC. 2fb + fa, 2fa – fb and 2fb – fa. The intermodulation distortion is defined as the ratio of the RMS value of either input tone to the RMS value of the largest 3rd order intermodulation product. Spurious Free Dynamic Range (SFDR) Spurious free dynamic range is the peak harmonic or spurious noise that is the largest spectral component excluding the input signal and DC. This value is expressed in decibels relative to the RMS value of a full scale input signal. Input Bandwidth The input bandwidth is that input frequency at which the amplitude of the reconstructed fundamental is reduced by 3dB for a full scale input signal. Total Harmonic Distortion Total harmonic distortion is the ratio of the RMS sum of all harmonics of the input signal to the fundamental itself. The out-of-band harmonics alias into the frequency band between DC and half the sampling frequency. THD is expressed as: THD = 20Log (√(V22 + V32 + V42 + . . . Vn2)/V1) where V1 is the RMS amplitude of the fundamental frequency and V2 through Vn are the amplitudes of the second through nth harmonics. The THD calculated in this data sheet uses all the harmonics up to the fifth. Aperture Delay Time The time from when CLK reaches midsupply to the instant that the input signal is held by the sample and hold circuit. Aperture Delay Jitter The variation in the aperture delay time from conversion to conversion. This random variation will result in noise when sampling an AC input. The signal to noise ratio due to the jitter alone will be: SNRJITTER = –20log (2π • fIN • tJITTER) Intermodulation Distortion Crosstalk If the ADC input signal consists of more than one spectral component, the ADC transfer function nonlinearity can produce intermodulation distortion (IMD) in addition to THD. IMD is the change in one sinusoidal input caused by the presence of another sinusoidal input at a different frequency. Crosstalk is the coupling from one channel (being driven by a full-scale signal) onto the other channel (being driven by a –1dBFS signal). If two pure sine waves of frequencies fa and fb are applied to the ADC input, nonlinearities in the ADC transfer function can create distortion products at the sum and difference frequencies of mfa ± nfb, where m and n = 0, 1, 2, 3, etc. The 3rd order intermodulation products are 2fa + fb, CONVERTER OPERATION As shown in Figure 1, the LTC2298/LTC2297/LTC2296 are dual CMOS pipelined multistep converters. The converters have six pipelined ADC stages; a sampled analog input will result in a digitized value five cycles later (see the Timing Diagram section). For optimal AC performance the analog inputs should be driven differentially. For cost 229876fa 15 LTC2298/LTC2297/LTC2296 U U W U APPLICATIO S I FOR ATIO sensitive applications, the analog inputs can be driven single-ended with slightly worse harmonic distortion. The CLK input is single-ended. The LTC2298/LTC2297/ LTC2296 have two phases of operation, determined by the state of the CLK input pin. Each pipelined stage shown in Figure 1 contains an ADC, a reconstruction DAC and an interstage residue amplifier. In operation, the ADC quantizes the input to the stage and the quantized value is subtracted from the input by the DAC to produce a residue. The residue is amplified and output by the residue amplifier. Successive stages operate out of phase so that when the odd stages are outputting their residue, the even stages are acquiring that residue and vice versa. When CLK is low, the analog input is sampled differentially directly onto the input sample-and-hold capacitors, inside the “Input S/H” shown in the block diagram. At the instant that CLK transitions from low to high, the sampled input is held. While CLK is high, the held input voltage is buffered by the S/H amplifier which drives the first pipelined ADC stage. The first stage acquires the output of the S/H during this high phase of CLK. When CLK goes back low, the first stage produces its residue which is acquired by the second stage. At the same time, the input S/H goes back to acquiring the analog input. When CLK goes back high, the second stage produces its residue which is acquired by the third stage. An identical process is repeated for the third, fourth and fifth stages, resulting in a fifth stage residue that is sent to the sixth stage ADC for final evaluation. Each ADC stage following the first has additional range to accommodate flash and amplifier offset errors. Results from all of the ADC stages are digitally synchronized such that the results can be properly combined in the correction logic before being sent to the output buffer. SAMPLE/HOLD OPERATION AND INPUT DRIVE Sample/Hold Operation Figure 2 shows an equivalent circuit for the LTC2298/ LTC2297/LTC2296 CMOS differential sample-and-hold. The analog inputs are connected to the sampling capacitors (CSAMPLE) through NMOS transistors. The capacitors shown attached to each input (CPARASITIC) are the summation of all other capacitance associated with each input. During the sample phase when CLK is low, the transistors connect the analog inputs to the sampling capacitors and they charge to and track the differential input voltage. When CLK transitions from low to high, the sampled input voltage is held on the sampling capacitors. During the hold phase when CLK is high, the sampling capacitors are disconnected from the input and the held voltage is passed to the ADC core for processing. As CLK transitions from high to low, the inputs are reconnected to the sampling LTC2298/LTC2297/LTC2296 VDD AIN+ CPARASITIC 1pF VDD AIN– CSAMPLE 4pF 15Ω CSAMPLE 4pF 15Ω CPARASITIC 1pF VDD CLK 229876 F02 Figure 2. Equivalent Input Circuit 229876fa 16 LTC2298/LTC2297/LTC2296 U W U U APPLICATIO S I FOR ATIO capacitors to acquire a new sample. Since the sampling capacitors still hold the previous sample, a charging glitch proportional to the change in voltage between samples will be seen at this time. If the change between the last sample and the new sample is small, the charging glitch seen at the input will be small. If the input change is large, such as the change seen with input frequencies near Nyquist, then a larger charging glitch will be seen. Single-Ended Input For cost sensitive applications, the analog inputs can be driven single-ended. With a single-ended input the harmonic distortion and INL will degrade, but the SNR and DNL will remain unchanged. For a single-ended input, AIN+ should be driven with the input signal and AIN– should be connected to 1.5V or VCM. Common Mode Bias For optimal performance the analog inputs should be driven differentially. Each input should swing ±0.5V for the 2V range or ±0.25V for the 1V range, around a common mode voltage of 1.5V. The VCM output pin may be used to provide the common mode bias level. VCM can be tied directly to the center tap of a transformer to set the DC input level or as a reference level to an op amp differential driver circuit. The VCM pin must be bypassed to ground close to the ADC with a 2.2µF or greater capacitor. glitch has been designed to be as linear as possible to minimize the effects of incomplete settling. For the best performance, it is recommended to have a source impedance of 100Ω or less for each input. The source impedance should be matched for the differential inputs. Poor matching will result in higher even order harmonics, especially the second. Input Drive Circuits Figure 3 shows the LTC2298/LTC2297/LTC2296 being driven by an RF transformer with a center tapped secondary. The secondary center tap is DC biased with VCM, setting the ADC input signal at its optimum DC level. Terminating on the transformer secondary is desirable, as this provides a common mode path for charging glitches caused by the sample and hold. Figure 3 shows a 1:1 turns ratio transformer. Other turns ratios can be used if the source impedance seen by the ADC does not exceed 100Ω for each ADC input. A disadvantage of using a transformer is the loss of low frequency response. Most small RF transformers have poor performance at frequencies below 1MHz. VCM 2.2µF 0.1µF ANALOG INPUT T1 1:1 25Ω 25Ω 0.1µF Input Drive Impedance As with all high performance, high speed ADCs, the dynamic performance of the LTC2298/LTC2297/LTC2296 can be influenced by the input drive circuitry, particularly the second and third harmonics. Source impedance and reactance can influence SFDR. At the falling edge of CLK, the sample-and-hold circuit will connect the 4pF sampling capacitor to the input pin and start the sampling period. The sampling period ends when CLK rises, holding the sampled input on the sampling capacitor. Ideally the input circuitry should be fast enough to fully charge the sampling capacitor during the sampling period 1/(2FENCODE); however, this is not always possible and the incomplete settling may degrade the SFDR. The sampling AIN+ LTC2298 LTC2297 LTC2296 12pF 25Ω T1 = MA/COM ETC1-1T 25Ω RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE AIN– 229876 F03 Figure 3. Single-Ended to Differential Conversion Using a Transformer Figure 4 demonstrates the use of a differential amplifier to convert a single ended input signal into a differential input signal. The advantage of this method is that it provides low frequency input response; however, the limited gain bandwidth of most op amps will limit the SFDR at high input frequencies. 229876fa 17 LTC2298/LTC2297/LTC2296 U W U U APPLICATIO S I FOR ATIO VCM HIGH SPEED DIFFERENTIAL 25Ω AMPLIFIER ANALOG INPUT + – 2.2µF AIN+ + CM VCM 2.2µF 0.1µF LTC2298 LTC2297 LTC2296 25Ω 25Ω 0.1µF AIN– AIN+ 0.1µF T1 12pF – 12Ω ANALOG INPUT LTC2298 LTC2297 LTC2296 8pF 25Ω 12Ω AIN– T1 = MA/COM, ETC 1-1-13 RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE 229876 F04 229876 F06 Figure 4. Differential Drive with an Amplifier Figure 5 shows a single-ended input circuit. The impedance seen by the analog inputs should be matched. This circuit is not recommended if low distortion is required. Figure 6. Recommended Front End Circuit for Input Frequencies Between 70MHz and 170MHz VCM 2.2µF VCM 1k 0.1µF ANALOG INPUT 1k 25Ω 0.1µF 25Ω AIN+ 0.1µF LTC2298 LTC2297 LTC2296 25Ω T1 = MA/COM, ETC 1-1-13 RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE AIN– 0.1µF 0.1µF T1 LTC2298 LTC2297 LTC2296 12pF 25Ω AIN+ ANALOG INPUT 2.2µF AIN– 229876 F07 229876 F05 Figure 7. Recommended Front End Circuit for Input Frequencies Between 170MHz and 300MHz Figure 5. Single-Ended Drive The 25Ω resistors and 12pF capacitor on the analog inputs serve two purposes: isolating the drive circuitry from the sample-and-hold charging glitches and limiting the wideband noise at the converter input. For input frequencies above 70MHz, the input circuits of Figure 6, 7 and 8 are recommended. The balun transformer gives better high frequency response than a flux coupled center tapped transformer. The coupling capacitors allow the analog inputs to be DC biased at 1.5V. In Figure 8, the series inductors are impedance matching elements that maximize the ADC bandwidth. VCM 2.2µF 0.1µF 6.8nH ANALOG INPUT 25Ω AIN+ 0.1µF LTC2298 LTC2297 LTC2296 T1 0.1µF 25Ω 6.8nH – AIN T1 = MA/COM, ETC 1-1-13 RESISTORS, CAPACITORS, INDUCTORS ARE 0402 PACKAGE SIZE 229876 F08 Figure 8. Recommended Front End Circuit for Input Frequencies Above 300MHz 229876fa 18 LTC2298/LTC2297/LTC2296 U W U U APPLICATIO S I FOR ATIO Reference Operation Figure 9 shows the LTC2298/LTC2297/LTC2296 reference circuitry consisting of a 1.5V bandgap reference, a difference amplifier and switching and control circuit. The internal voltage reference can be configured for two pin selectable input ranges of 2V (±1V differential) or 1V (±0.5V differential). Tying the SENSE pin to VDD selects the 2V range; tying the SENSE pin to VCM selects the 1V range. The 1.5V bandgap reference serves two functions: its output provides a DC bias point for setting the common mode voltage of any external input circuitry; additionally, the reference is used with a difference amplifier to generate the differential reference levels needed by the internal ADC circuitry. An external bypass capacitor is required for the 1.5V reference output, VCM. This provides a high frequency low impedance path to ground for internal and external circuitry. The difference amplifier generates the high and low reference for the ADC. High speed switching circuits are connected to these outputs and they must be externally bypassed. Each output has two pins. The multiple output pins are needed to reduce package inductance. Bypass capacitors must be connected as shown in Figure 9. Each ADC channel has an independent reference with its own bypass capacitors. The two channels can be used with the same or different input ranges. Other voltage ranges between the pin selectable ranges can be programmed with two external resistors as shown in Figure 10. An external reference can be used by applying its output directly or through a resistor divider to SENSE. It is not recommended to drive the SENSE pin with a logic device. The SENSE pin should be tied to the appropriate level as close to the converter as possible. If the SENSE pin is driven externally, it should be bypassed to ground as close to the device as possible with a 1µF ceramic capacitor. For the best channel matching, connect an external reference to SENSEA and SENSEB. LTC2298/LTC2297/LTC2296 1.5V VCM 4Ω 1.5V 1.5V BANDGAP REFERENCE 2.2µF 2.2µF 12k 0.5V 1V 0.75V TIE TO VDD FOR 2V RANGE; TIE TO VCM FOR 1V RANGE; RANGE = 2 • VSENSE FOR 0.5V < VSENSE < 1V RANGE DETECT AND CONTROL 12k BUFFER 0.1µF LTC2298 LTC2297 LTC2296 1µF Figure 10. 1.5V Range ADC INTERNAL ADC HIGH REFERENCE Input Range REFH 2.2µF SENSE 229876 F10 SENSE 1µF VCM The input range can be set based on the application. The 2V input range will provide the best signal-to-noise performance while maintaining excellent SFDR. The 1V input range will have better SFDR performance, but the SNR will degrade by 5.8dB. See the Typical Performance Characteristics section. DIFF AMP 1µF REFL INTERNAL ADC LOW REFERENCE 229876 F09 Figure 9. Equivalent Reference Circuit Driving the Clock Input The CLK inputs can be driven directly with a CMOS or TTL level signal. A sinusoidal clock can also be used along with a low jitter squaring circuit before the CLK pin (Figure 11). 229876fa 19 LTC2298/LTC2297/LTC2296 U W U U APPLICATIO S I FOR ATIO CLEAN SUPPLY 4.7µF SINUSOIDAL CLOCK INPUT 0.1µF 4.7µF FERRITE BEAD FERRITE BEAD 0.1µF 0.1µF 1k CLK 50Ω 1k CLEAN SUPPLY LTC2298 LTC2297 LTC2296 CLK 100Ω NC7SVU04 LTC2298 LTC2297 LTC2296 229876 F11 Figure 11. Sinusoidal Single-Ended CLK Drive The noise performance of the LTC2298/LTC2297/LTC2296 can depend on the clock signal quality as much as on the analog input. Any noise present on the clock signal will result in additional aperture jitter that will be RMS summed with the inherent ADC aperture jitter. In applications where jitter is critical, such as when digitizing high input frequencies, use as large an amplitude as possible. Also, if the ADC is clocked with a sinusoidal signal, filter the CLK signal to reduce wideband noise and distortion products generated by the source. It is recommended that CLKA and CLKB are shorted together and driven by the same clock source. If a small time delay is desired between when the two channels sample the analog inputs, CLKA and CLKB can be driven by two different signals. If this delay exceeds 1ns, the performance of the part may degrade. CLKA and CLKB should not be driven by asynchronous signals. Figures 12 and 13 show alternatives for converting a differential clock to the single-ended CLK input. The use of a transformer provides no incremental contribution to phase noise. The LVDS or PECL to CMOS translators provide little degradation below 70MHz, but at 140MHz will degrade the SNR compared to the transformer solution. The nature of the received signals also has a large bearing on how much SNR degradation will be experienced. For high crest factor signals such as WCDMA or OFDM, where the nominal power level must be at least 6dB to 8dB below full scale, the use of these translators will have a lesser impact. 229876 F12 IF LVDS USE FIN1002 OR FIN1018. FOR PECL, USE AZ1000ELT21 OR SIMILAR Figure 12. CLK Drive Using an LVDS or PECL to CMOS Converter ETC1-1T CLK 5pF-30pF DIFFERENTIAL CLOCK INPUT LTC2298 LTC2297 LTC2296 229876 F13 0.1µF FERRITE BEAD VCM Figure 13. LVDS or PECL CLK Drive Using a Transformer The transformer in the example may be terminated with the appropriate termination for the signaling in use. The use of a transformer with a 1:4 impedance ratio may be desirable in cases where lower voltage differential signals are considered. The center tap may be bypassed to ground through a capacitor close to the ADC if the differential signals originate on a different plane. The use of a capacitor at the input may result in peaking, and depending on transmission line length may require a 10Ω to 20Ω ohm series resistor to act as both a low pass filter for high frequency noise that may be induced into the clock line by neighboring digital signals, as well as a damping mechanism for reflections. 229876fa 20 LTC2298/LTC2297/LTC2296 Maximum and Minimum Conversion Rates The maximum conversion rate for the LTC2298/LTC2297/ LTC2296 is 65Msps (LTC2298), 40Msps (LTC2297), and 25Msps (LTC2296). For the ADC to operate properly, the CLK signal should have a 50% (±5%) duty cycle. Each half cycle must have at least 7.3ns (LTC2298), 11.8ns (LTC2297), and 18.9ns (LTC2296) for the ADC internal circuitry to have enough settling time for proper operation. An optional clock duty cycle stabilizer circuit can be used if the input clock has a non 50% duty cycle. This circuit uses the rising edge of the CLK pin to sample the analog input. The falling edge of CLK is ignored and the internal falling edge is generated by a phase-locked loop. The input clock duty cycle can vary from 40% to 60% and the clock duty cycle stabilizer will maintain a constant 50% internal duty cycle. If the clock is turned off for a long period of time, the duty cycle stabilizer circuit will require a hundred clock cycles for the PLL to lock onto the input clock. To use the clock duty cycle stabilizer, the MODE pin should be connected to 1/3VDD or 2/3VDD using external resistors. The MODE pin controls both Channel A and Channel B—the duty cycle stabilizer is either on of off for both channels. The lower limit of the LTC2298/LTC2297/LTC2296 sample rate is determined by droop of the sample-and-hold circuits. The pipelined architecture of this ADC relies on storing analog signals on small valued capacitors. Junction leakage will discharge the capacitors. The specified minimum operating frequency for the LTC2298/LTC2297/ LTC2296 is 1Msps. Table 1. Output Codes vs Input Voltage AIN+ – AIN– (2V Range) OF D13 – D0 (Offset Binary) D13 – D0 (2’s Complement) >+1.000000V +0.999878V +0.999756V 1 0 0 11 1111 1111 1111 11 1111 1111 1111 11 1111 1111 1110 01 1111 1111 1111 01 1111 1111 1111 01 1111 1111 1110 +0.000122V 0.000000V –0.000122V –0.000244V 0 0 0 0 10 0000 0000 0001 10 0000 0000 0000 01 1111 1111 1111 01 1111 1111 1110 00 0000 0000 0001 00 0000 0000 0000 11 1111 1111 1111 11 1111 1111 1110 –0.999878V –1.000000V