LTC2233IUK#PBF

LTC2232/LTC2233 10-Bit,105Msps/ 80Msps ADCs U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO Sample Rate: 105Msps/80Msps 61dB SNR up to 140MHz Input 75dB SFDR up to 200MHz Input 775MHz Full Power Bandwidth S/H Single 3.3V Supply Low Power Dissipation: 475mW/366mW Selectable Input Ranges: ±0.5V or ±1V No Missing Codes Optional Clock Duty Cycle Stabilizer Shutdown and Nap Modes Data Ready Output Clock Pin Compatible Family 135Msps: LTC2224 (12-Bit), LTC2234 (10-Bit) 105Msps: LTC2222 (12-Bit), LTC2232 (10-Bit) 80Msps: LTC2223 (12-Bit), LTC2233 (10-Bit) 48-Pin 7mm x 7mm QFN Package U APPLICATIO S ■ ■ ■ ■ Wireless and Wired Broadband Communication Cable Head-End Systems Power Amplifier Linearization Communications Test Equipment The LTC®2232 and LTC2233 are 105Msps/80Msps, sampling 10-bit A/D converters designed for digitizing high frequency, wide dynamic range signals. The LTC2232/ LTC2233 are perfect for demanding communications applications with AC performance that includes 61dB SNR and 75dB spurious free dynamic range for signals up to 200MHz. Ultralow jitter of 0.15psRMS allows undersampling of IF frequencies with excellent noise performance. DC specs include ±0.15LSB INL (typ), ±0.1LSB DNL (typ) and ±0.8LSB INL, ±0.6LSB DNL over temperature. The transition noise is a low 0.12LSBRMS. A separate output power supply allows the outputs to drive 0.5V to 3.6V logic. The ENC+ and ENC – inputs may be driven differentially or single ended with a sine wave, PECL, LVDS, TTL, or CMOS inputs. 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 TYPICAL APPLICATIO 3.3V VDD REFH REFL SFDR vs Input Frequency 0.5V TO 3.6V FLEXIBLE REFERENCE 90 85 4th OR HIGHER OVDD ANALOG INPUT INPUT S/H – 10-BIT PIPELINED ADC CORE CORRECTION LOGIC D9 • • • D0 OUTPUT DRIVERS SFDR (dBFS) + 80 75 70 2nd OR 3rd 65 60 OGND CLOCK/DUTY CYCLE CONTROL 55 50 0 100 200 300 400 500 600 INPUT FREQUENCY (MHz) 22323 TA01b 22323 TA01 ENCODE INPUT 22323fa 1 LTC2232/LTC2233 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO OVDD = VDD (Notes 1, 2) TOP VIEW 48 GND 47 VDD 46 VDD 45 GND 44 VCM 43 SENSE 42 MODE 41 OF 40 D9 39 D8 38 OGND 37 OVDD 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 LTC2232C, LTC2233C ............................. 0°C to 70°C LTC2232I, LTC2233I ...........................–40°C to 85°C Storage Temperature Range ..................–65°C to 125°C AIN+ 1 AIN– 2 REFHA 3 REFHA 4 REFLB 5 REFLB 6 REFHB 7 REFHB 8 REFLA 9 REFLA 10 VDD 11 VDD 12 36 D7 35 D6 34 D5 33 OVDD 32 OGND 31 D4 30 D3 29 D2 28 OVDD 27 OGND 26 D1 25 D0 GND 13 VDD 14 GND 15 ENC + 16 ENC – 17 SHDN 18 OE 19 CLOCKOUT 20 NC 21 OGND 22 OVDD 23 NC 24 49 UK PACKAGE 48-LEAD (7mm × 7mm) PLASTIC QFN EXPOSED PAD IS GND (PIN 49), MUST BE SOLDERED TO PCB TJMAX = 125°C, θJA = 29°C/W ORDER PART NUMBER UK PART MARKING* LTC2232CUK LTC2232IUK LTC2233CUK LTC2233IUK LTC2232UK LTC2232UK LTC2233UK LTC2233UK 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/ *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for parts specified with wider operating temperature ranges. 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 CONDITIONS MIN TYP MAX UNITS ● 10 Integral Linearity Error (Note 5) Differential Analog Input ● –0.8 ±0.15 0.8 LSB Differential Linearity Error Differential Analog Input ● –0.6 ±0.1 0.6 LSB Resolution (No Missing Codes) Bits Integral Linearity Error (Note 5) Single-Ended Analog Input ±0.5 LSB Differential Linearity Error Single-Ended Analog Input ±0.1 LSB Offset Error (Note 6) Gain Error External Reference Offset Drift ● –37 ±5 37 ● –2.5 ±0.5 2.5 mV %FS ±10 µV/C Full-Scale Drift Internal Reference External Reference ±30 ±15 ppm/C ppm/C Transition Noise SENSE = 1V 0.12 LSBRMS 22323fa 2 LTC2232/LTC2233 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 CONDITIONS VIN Analog Input Range (AIN+ – AIN–) 3.1V < VDD < 3.5V ● VIN, CM Analog Input Common Mode (AIN+ Differential Input Single Ended Input (Note 7) ● ● 1 0.5 IIN Analog Input Leakage Current 0 < AIN+, AIN– < VDD ● ISENSE SENSE Input Leakage 0V < SENSE < 1V ● IMODE MODE Pin Pull-Down Current to GND + AIN–)/2 Full Power Bandwidth MIN TYP MAX UNITS ±0.5 to ±1 1.6 1.6 V 1.9 2.1 V V –1 1 µA –1 1 µA Figure 8 Test Circuit 10 µA 775 MHz tAP Sample and Hold Acquisition Delay Time 0 tJITTER Sample and Hold Acquisition Delay Time Jitter 0.15 CMRR Analog Input Common Mode Rejection Ratio 80 ns psRMS dB 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 30MHz Input (1V Range) 30MHz Input (2V Range) SFDR SFDR S/(N+D) Spurious Free Dynamic Range Spurious Free Dynamic Range 4th Harmonic or Higher Signal-to-Noise Plus Distortion Ratio Intermodulation Distortion ● 60.4 LTC2232 TYP MAX 59.8 61.3 MIN 60.4 LTC2233 TYP MAX UNITS 59.9 61.3 dB dB 70MHz Input (1V Range) 70MHz Input (2V Range) 59.8 61.2 59.8 61.3 dB dB 140MHz Input (1V Range) 140MHz Input (2V Range) 59.8 61.2 59.8 61.2 dB dB 250MHz Input (1V Range) 250MHz Input (2V Range) 59.6 61.1 59.7 61.2 dB dB 80 78 dB dB 30MHz Input (1V Range) 30MHz Input (2V Range) ● 69 80 78 69 70MHz Input (1V Range) 70MHz Input (2V Range) 80 78 80 78 dB dB 140MHz Input (1V Range) 140MHz Input (2V Range) 78 78 78 78 dB dB 250MHz Input (1V Range) 250MHz Input (2V Range) 71 70 73 72 dB dB 30MHz Input (1V Range) 30MHz Input (2V Range) 86 86 86 86 dB dB 70MHz Input (1V Range) 70MHz Input (2V Range) 86 86 86 86 dB dB 140MHz Input (1V Range) 140MHz Input (2V Range) 86 86 86 86 dB dB 250MHz Input (1V Range) 250MHz Input (2V Range) 86 86 86 86 dB dB 59.9 61.3 dB dB 59.8 61.2 59.8 61.2 dB dB 81 81 dBc 30MHz Input (1V Range) 30MHz Input (2V Range) 70MHz Input (1V Range) 70MHz Input (2V Range) IMD MIN fIN1 = 138MHz, fIN2 = 140MHz ● 60.2 59.8 61.3 60.2 22323fa 3 LTC2232/LTC2233 U U U I TER AL REFERE CE CHARACTERISTICS (Note 4) PARAMETER CONDITIONS MIN TYP MAX VCM Output Voltage IOUT = 0 1.570 1.600 1.630 ±25 VCM Output Tempco UNITS V ppm/°C VCM Line Regulation 3.1V < VDD < 3.5V 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 2.5 V V ENCODE INPUTS (ENC +, ENC –) VID Differential Input Voltage VICM Common Mode Input Voltage RIN Input Resistance CIN Input Capacitance ● Internally Set Externally Set (Note 7) ● 0.2 1.1 (Note 7) V 1.6 1.6 6 kΩ 3 pF LOGIC INPUTS (OE, SHDN) VIH High Level Input Voltage VDD = 3.3V ● VIL Low Level Input Voltage VDD = 3.3V ● 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 = 3.3V COZ Hi-Z Output Capacitance OE = High (Note 7) 3 pF ISOURCE Output Source Current VOUT = 0V 50 mA ISINK Output Sink Current VOUT = 3.3V 50 mA VOH High Level Output Voltage IO = –10µA IO = –200µA ● IO = 10µA IO = 1.6mA ● VOL Low Level Output Voltage 3.1 3.295 3.29 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 22323fa 4 LTC2232/LTC2233 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 9) CONDITIONS MIN LTC2232 TYP MAX PARAMETER VDD Analog Supply Voltage ● 3.1 OVDD Output Supply Voltage ● 0.5 IVDD Analog Supply Current ● PDISS Power Dissipation ● 475 PSHDN Shutdown Power SHDN = H, OE = H, No CLK 2 2 mW PNAP Nap Mode Power SHDN = H, OE = L, No CLK 35 35 mW 3.3 MIN LTC2233 TYP MAX SYMBOL 3.3 UNITS 3.5 3.1 3.5 V 3.3 3.6 0.5 3.3 3.6 V 144 162 111 123 mA 535 366 406 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) SYMBOL PARAMETER fS Sampling Frequency tL ENC Low Time (Note 8) tH ENC High Time (Note 8) tAP Sample-and-Hold Aperture Delay tD tC tOE CONDITIONS MIN ● 1 Duty Cycle Stabilizer Off Duty Cycle Stabilizer On ● ● 4.5 3 Duty Cycle Stabilizer Off Duty Cycle Stabilizer On ● ● ENC to DATA Delay (Note 7) ENC to CLOCKOUT Delay LTC2232 TYP MAX MIN 105 1 4.76 4.76 500 500 5.9 3 4.5 3 4.76 4.76 500 500 ● 1.3 2.1 (Note 7) ● 1.3 DATA to CLOCKOUT Skew (tC - tD) (Note 7) ● – 0.6 Output Enable Delay (Note 7) ● 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 = 3.3V, fSAMPLE = 105MHz (LTC2232) or 80MHz (LTC2233), differential ENC+/ENC– = 2VP-P sine wave, input range = 2VP-P with differential drive, unless otherwise noted. UNITS 80 MHz 6.25 6.25 500 500 ns ns 5.9 3 6.25 6.25 500 500 ns ns 4 1.3 2.1 4 ns 2.1 4 1.3 2.1 4 ns 0 0.6 –0.6 0 0.6 ns 5 10 5 10 ns 0 Pipeline Latency LTC2233 TYP MAX 5 0 5 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 and 11 1111 1111 in 2’s complement output mode. Note 7: Guaranteed by design, not subject to test. Note 8: Recommended operating conditions. Note 9: VDD = 3.3V, fSAMPLE = 105MHz (LTC2232) or 80MHz (LTC2233), differential ENC+/ENC– = 2VP-P sine wave, input range = 1VP-P with differential drive. 22323fa 5 LTC2232/LTC2233 U W TYPICAL PERFOR A CE CHARACTERISTICS LTC2232: SNR vs Input Frequency, –1dB, 2V Range LTC2232: DNL, 2V Range 1.0 65 0.8 0.8 64 0.6 0.6 63 0.4 0.4 62 0.2 0 – 0.2 SNR (dBFS) 1.0 ERROR (LSB) ERROR (LSB) LTC2232: INL, 2V Range 0.2 0 – 0.2 61 60 59 – 0.4 – 0.4 58 – 0.6 – 0.6 57 – 0.8 – 0.8 56 – 1.0 – 1.0 256 0 768 512 OUTPUT CODE 1024 256 0 2232 G01 LTC2232: SNR vs Input Frequency, –1dB, 1V Range 768 512 OUTPUT CODE 55 1024 LTC2232: SFDR (HD2 and HD3) vs Input Frequency, –1dB, 2V Range 100 200 300 400 500 600 2232 G03 INPUT FREQUENCY (MHz) LTC2232: SFDR (HD2 and HD3) vs Input Frequency, –1dB, 1V Range 65 90 90 64 85 85 80 80 75 75 63 0 2232 G02 61 60 59 58 SFDR (dBFS) SFDR (dBFS) SNR (dBFS) 62 70 65 70 65 60 60 55 55 57 56 55 0 100 50 300 400 500 600 200 2232 G04 INPUT FREQUENCY (MHz) 100 50 200 300 400 500 600 2232 G05 INPUT FREQUENCY (MHz) 90 85 85 85 80 80 80 75 75 65 70 65 60 60 55 55 50 0 100 200 300 400 500 600 2232 G07 INPUT FREQUENCY (MHz) SFDR AND SNR (dBFS) 90 70 50 0 100 200 300 400 500 600 2232 G06 INPUT FREQUENCY (MHz) LTC2232: SFDR and SNR vs Sample Rate, 2V Range, fIN = 30MHz, –1dB LTC2232: SFDR (HD4+) vs Input Frequency, –1dB, 1V Range SFDR (dBFS) SFDR (dBFS) LTC2232: SFDR (HD4+) vs Input Frequency, –1dB, 2V Range 0 SFDR 75 70 65 SNR 60 55 50 0 100 200 300 400 500 600 2232 G08 INPUT FREQUENCY (MHz) 0 20 40 60 80 100 SAMPLE RATE (Msps) 120 2232 G09 22323fa 6 LTC2232/LTC2233 U W TYPICAL PERFOR A CE CHARACTERISTICS LTC2232: SFDR and SNR vs Sample Rate, 1V Range, fIN = 30MHz, –1dB S LTC2232: IOVDD vs Sample Rate, 5MHz Sine Wave Input, –1dB, OVDD = 1.8V LTC2232: IVDD vs Sample Rate, 5MHz Sine Wave Input, –1dB 160 85 10 SFDR 150 70 130 1V RANGE SNR 4 20 0 40 60 2 110 80 100 SAMPLE RATE (Msps) 100 120 0 20 2232 G10 LTC2232: SFDR vs Input Level, f IN = 70MHz, 2V Range 60 80 40 SAMPLE RATE (Msps) 100 0 120 0 – 10 – 10 – 20 – 20 – 30 – 30 – 40 – 40 AMPLITUDE (dB) dBc 50 40 30 – 50 – 60 – 70 – 80 – 40 –30 – 20 – 10 INPUT LEVEL (dBFS) – 80 – 90 – 110 – 110 0 5 2232 G13 LTC2232: 8192 Point FFT, f IN = 30MHz, –1dB, 2V Range 10 15 20 25 30 35 40 45 50 2232 G14 FREQUENCY (MHz) – 120 – 20 – 20 – 20 – 30 – 30 – 30 – 40 – 40 – 40 – 70 – 80 AMPLITUDE (dB) 0 – 10 AMPLITUDE (dB) 0 – 10 – 50 – 60 – 70 – 80 – 60 – 70 – 80 – 90 – 90 – 100 – 100 – 100 – 110 – 110 – 110 – 120 – 120 5 10 15 20 25 30 35 40 45 50 2232 G16 FREQUENCY (MHz) 0 5 10 15 20 25 30 35 40 45 50 2232 G17 FREQUENCY (MHz) 10 15 20 25 30 35 40 45 50 2232 G15 FREQUENCY (MHz) – 50 – 90 0 5 LTC2232: 8192 Point FFT, f IN = 70MHz, –1dB, 2V Range 0 – 60 0 LTC2232: 8192 Point FFT, f IN = 30MHz, –1dB, 1V Range – 10 – 50 120 2232 G12 – 70 – 100 0 100 – 60 – 100 – 120 0 – 50 40 60 80 SAMPLE RATE (Msps) – 50 – 90 20 10 AMPLITUDE (dB) 0 80 60 20 LTC2232: 8192 Point FFT, f IN = 5MHz, –1dB,1V Range 90 dBFS 0 2232 G11 LTC2232: 8192 Point FFT, f IN = 5MHz, –1dB, 2V Range 70 SFDR (dBc AND dBFS) 6 120 65 55 IOVDD (mA) 140 75 60 AMPLITUDE (dB) 8 2V RANGE IVDD (mA) SFDR AND SNR (dBFS) 80 – 120 0 5 10 15 20 25 30 35 40 45 50 2232 G18 FREQUENCY (MHz) 22323fa 7 LTC2232/LTC2233 U W TYPICAL PERFOR A CE CHARACTERISTICS LTC2232: 8192 Point FFT, f IN = 140MHz, –1dB, 2V Range LTC2232: 8192 Point FFT, f IN = 140MHz, –1dB, 1V Range 0 0 –10 –10 –20 –20 –20 –30 –30 –30 –40 –40 –40 –50 –60 –70 –80 AMPLITUDE (dB) 0 –10 AMPLITUDE (dB) AMPLITUDE (dB) LTC2232: 8192 Point FFT, f IN = 70MHz, –1dB, 1V Range –50 –60 –70 –80 –50 –60 –70 –80 –90 –90 –90 –100 –100 –100 –110 –110 –110 –120 –120 0 5 10 15 20 25 30 35 40 45 50 2232 G19 FREQUENCY (MHz) 5 –120 10 15 20 25 30 35 40 45 50 2232 G20 FREQUENCY (MHz) LTC2232: 8192 Point FFT, f IN = 250MHz, –1dB, 1V Range LTC2232: 8192 Point FFT, f IN = 250MHz, –1dB, 2V Range 0 0 –10 –10 –20 –20 –20 –30 –30 –30 –40 –40 –40 –60 –70 –80 AMPLITUDE (dB) 0 –50 –50 –60 –70 –80 –70 –80 –90 –100 –100 –100 –110 –110 –110 –120 –120 0 –10 –20 –20 –30 –30 –40 –40 AMPLITUDE (dB) AMPLITUDE (dB) 0 –10 –60 –70 –80 10 15 20 25 30 35 40 45 50 2232 G24 FREQUENCY (MHz) LTC2232: Shorted Input Noise Histogram 131071 100000 80000 60000 –80 –100 –110 –110 10 15 20 25 30 35 40 45 50 2232 G25 FREQUENCY (MHz) 5 120000 –70 –100 5 0 140000 –60 –90 0 –120 10 15 20 25 30 35 40 45 50 2232 G23 FREQUENCY (MHz) –50 –90 –120 5 LTC2232: 8192 Point 2-Tone FFT, f IN = 138MHz and 140MHz, –7dB Each, 1V Range LTC2232: 8192 Point 2-Tone FFT, f IN = 68MHz and 70MHz, –7dB Each, 2V Range –50 0 COUNT 10 15 20 25 30 35 40 45 50 2232 G22 FREQUENCY (MHz) 10 15 20 25 30 35 40 45 50 2232 G21 FREQUENCY (MHz) –60 –90 5 5 –50 –90 0 0 LTC2232: 8192 Point FFT, f IN = 500MHz, –6dB, 1V Range –10 AMPLITUDE (dB) AMPLITUDE (dB) 0 –120 40000 20000 0 0 5 10 15 20 25 30 35 40 45 50 2232 G26 FREQUENCY (MHz) 1 0 510 511 CODE 512 2232 G27 22323fa 8 LTC2232/LTC2233 U W TYPICAL PERFOR A CE CHARACTERISTICS LTC2233: SNR vs Input Frequency, –1dB, 2V Range LTC2233: DNL, 2V Range 1.0 65 0.8 0.8 64 0.6 0.6 63 0.4 0.4 62 0.2 0 –0.2 SNR (dBFS) 1.0 ERROR (LSB) ERROR (LSB) LTC2233: INL, 2V Range 0.2 0 –0.2 61 60 59 –0.4 –0.4 58 –0.6 –0.6 57 –0.8 –0.8 56 –1.0 –1.0 256 0 768 512 OUTPUT CODE 1024 256 0 2232 G01 768 512 OUTPUT CODE 55 1024 65 90 90 64 85 85 80 80 75 75 63 100 300 400 500 600 200 2232 G03 INPUT FREQUENCY (MHz) LTC2233: SFDR (HD2 and HD3) vs Input Frequency, –1dB, 1V Range LTC2233: SFDR (HD2 and HD3) vs Input Frequency, –1dB, 2V Range LTC2233: SNR vs Input Frequency, –1dB, 1V Range 0 2232 G02 61 60 59 58 SFDR (dBFS) SFDR (dBFS) SNR (dBFS) 62 70 65 70 65 60 60 55 55 57 56 55 0 100 50 300 400 500 600 200 2232 G04 INPUT FREQUENCY (MHz) 100 50 200 300 400 500 600 2232 G05 INPUT FREQUENCY (MHz) 90 85 85 85 80 80 80 75 75 65 70 65 60 60 55 55 50 0 100 200 300 400 500 600 2232 G07 INPUT FREQUENCY (MHz) SFDR AND SNR (dBFS) 90 70 50 0 100 200 300 400 500 600 2232 G06 INPUT FREQUENCY (MHz) LTC2233: SFDR and SNR vs Sample Rate, 2V Range, fIN = 30MHz, –1dB LTC2233: SFDR (HD4+) vs Input Frequency, –1dB, 1V Range SFDR (dBFS) SFDR (dBFS) LTC2233: SFDR (HD4+) vs Input Frequency, –1dB, 2V Range 0 SFDR 75 70 65 SNR 60 55 50 0 100 200 300 400 500 600 2232 G08 INPUT FREQUENCY (MHz) 0 20 40 60 80 100 SAMPLE RATE (Msps) 120 2232 G09 22323fa 9 LTC2232/LTC2233 U W TYPICAL PERFOR A CE CHARACTERISTICS LTC2233: SFDR and SNR vs Sample Rate, 1V Range, fIN = 30MHz, –1dB LTC2233: IOVDD vs Sample Rate, 5MHz Sine Wave Input, –1dB, OVDD = 1.8V LTC2233: IVDD vs Sample Rate, 5MHz Sine Wave Input, –1dB 85 8 130 SFDR 80 6 70 65 IOVDD (mA) 2V RANGE IVDD (mA) SFDR AND SNR (dBFS) 120 75 110 1V RANGE 100 4 SNR 60 2 90 55 50 80 0 40 60 80 SAMPLE RATE (Msps) 20 20 0 100 60 80 40 SAMPLE RATE (Msps) 2233 G10 0 –10 –10 –20 –20 –30 –30 –40 –40 dBFS AMPLITUDE (dB) 40 30 –60 –70 –80 –40 –30 –20 –10 INPUT LEVEL (dBFS) –60 –70 –80 –90 –100 –100 –110 –110 –120 0 –50 –50 –90 20 10 –50 0 0 5 10 2233 G13 LTC2233: 8192 Point FFT, f IN = 30MHz, –1dB, 2V Range 15 20 25 30 FREQUENCY (MHz) 35 40 –120 LTC2233: 8192 Point FFT, f IN = 30MHz, –1dB, 1V Range 0 0 –10 –10 –20 –20 –20 –30 –30 –30 –40 –40 –40 AMPLITUDE (dB) 0 –60 –70 –80 –50 –60 –70 –80 –90 –100 –110 –110 –110 –120 –120 35 40 2233 G16 0 5 10 15 20 25 30 FREQUENCY (MHz) 40 2233 G15 –80 –100 15 20 25 30 FREQUENCY (MHz) 35 –70 –100 10 15 20 25 30 FREQUENCY (MHz) –60 –90 5 10 –50 –90 0 5 LTC2233: 8192 Point FFT, f IN = 70MHz, –1dB, 2V Range –10 –50 0 2233 G14 AMPLITUDE (dB) SFDR (dBc AND dBFS) 70 AMPLITUDE (dB) 0 80 50 100 LTC2233: 8192 Point FFT, f IN = 5MHz, –1dB, 1V Range 90 dBc 60 80 40 SAMPLE RATE (Msps) 2233 G12 LTC2233: 8192 Point FFT, f IN = 5MHz, –1dB, 2V Range 60 20 0 2233 G11 LTC2233: SFDR vs Input Level, f IN = 70MHz, 2V Range AMPLITUDE (dB) 0 100 35 40 2233 G17 –120 0 5 10 15 20 25 30 FREQUENCY (MHz) 35 40 2233 G18 22323fa 10 LTC2232/LTC2233 U W TYPICAL PERFOR A CE CHARACTERISTICS LTC2233: 8192 Point FFT, f IN = 140MHz, –1dB, 2V Range LTC2233: 8192 Point FFT, f IN = 140MHz, –1dB, 1V Range 0 0 –10 –10 –20 –20 –20 –30 –30 –30 –40 –40 –40 –50 –60 –70 –80 AMPLITUDE (dB) 0 –10 AMPLITUDE (dB) AMPLITUDE (dB) LTC2233: 8192 Point FFT, f IN = 70MHz, –1dB, 1V Range –50 –60 –70 –80 –50 –60 –70 –80 –90 –90 –90 –100 –100 –100 –110 –110 –110 –120 –120 0 5 10 15 20 25 30 FREQUENCY (MHz) 35 40 5 10 2233 G19 LTC2233: 8192 Point FFT, f IN = 250MHz, –1dB, 2V Range 15 20 25 30 FREQUENCY (MHz) 35 –120 40 0 0 –10 –10 –20 –20 –20 –30 –30 –30 –40 –40 –40 –70 –80 AMPLITUDE (dB) 0 –60 –50 –60 –70 –80 –80 –90 –100 –100 –110 –110 –110 –120 –120 35 40 0 –10 –20 –20 –30 –30 –40 –40 AMPLITUDE (dB) AMPLITUDE (dB) 0 –50 –60 –70 –80 –100 –110 –120 –120 40 0 10 5 2233 G23 15 20 25 30 FREQUENCY (MHz) 35 40 2233 G24 LTC2233: Shorted Input Noise Histogram 140000 131071 120000 100000 –80 –110 2233 G25 –120 40 –70 –100 35 35 –60 –90 15 20 25 30 FREQUENCY (MHz) 15 20 25 30 FREQUENCY (MHz) –50 –90 10 10 LTC2233: 8192 Point 2-Tone FFT, f IN = 138MHz and 140MHz, –7dB Each, 1V Range –10 5 5 2233 G22 LTC2233: 8192 Point 2-Tone FFT, f IN = 68MHz and 70MHz, –7dB Each, 2V Range 0 0 COUNT 15 20 25 30 FREQUENCY (MHz) 40 2233 G21 –70 –100 10 35 –60 –90 5 15 20 25 30 FREQUENCY (MHz) –50 –90 0 10 5 LTC2233: 8192 Point FFT, f IN = 500MHz, –6dB, 1V Range –10 –50 0 2233 G20 LTC2233: 8192 Point FFT, f IN = 250MHz, –1dB, 1V Range AMPLITUDE (dB) AMPLITUDE (dB) 0 80000 60000 40000 20000 0 1 0 0 5 10 15 20 25 30 FREQUENCY (MHz) 35 40 2233 G26 510 511 CODE 512 2233 G27 22323fa 11 LTC2232/LTC2233 U U U PI FU CTIO S AIN+ (Pin 1): Positive Differential Analog Input. AIN– (Pin 2): Negative Differential Analog Input. REFHA (Pins 3, 4): ADC High Reference. Bypass to Pins 5, 6 with 0.1µF ceramic chip capacitor, to Pins 9, 10 with a 2.2µF ceramic capacitor and to ground with a 1µF ceramic capacitor. REFLB (Pins 5, 6): ADC Low Reference. Bypass to Pins 5, 6 with 0.1µF ceramic chip capacitor. Do not connect to Pins 9, 10. REFHB (Pins 7, 8): ADC High Reference. Bypass to Pins 9, 10 with 0.1µF ceramic chip capacitor. Do not connect to Pins 3, 4. REFLA (Pins 9, 10): ADC Low Reference. Bypass to Pins 7, 8 with 0.1µF ceramic chip capacitor, to Pins 3, 4 with a 2.2µF ceramic capacitor and to ground with a 1µF ceramic capacitor. VDD (Pins 11, 12, 14, 46, 47): 3.3V Supply. Bypass to GND with 0.1µF ceramic chip capacitors. Adjacent pins can share a bypass capacitor. GND (Pins 13, 15, 45, 48): ADC Power Ground. ENC+ (Pin 16): Encode Input. The input is sampled on the positive edge. ENC– (Pin 17): Encode Complement Input. The input is sampled on the negative edge. Bypass to ground with 0.1µF ceramic for single-ended ENCODE signal. SHDN (Pin 18): Shutdown Mode Selection Pin. Connecting SHDN to GND and OE to GND results in normal operation with the outputs enabled. Connecting SHDN to GND and OE to VDD results in normal operation with the outputs at high impedance. Connecting SHDN to VDD and OE to GND results in nap mode with the outputs at high impedance. Connecting SHDN to VDD and OE to VDD results in sleep mode with the outputs at high impedance. OE (Pin 19): Output Enable Pin. Refer to SHDN pin function. CLOCKOUT (Pin 20): Data Valid Output. Latch data on the falling edge of CLKOUT. NC (Pins 21, 24): Do not connect these pins. D0 – D9 (Pins 25, 26, 29, 30, 31, 34, 35, 36, 39, 40): Digital Outputs. D9 is the MSB. OGND (Pins 22, 27, 32, 38): Output Driver Ground. OVDD (Pins 23, 28, 33, 37): Positive Supply for the Output Drivers. Bypass to ground with 0.1µF ceramic chip capacitors. OF (Pin 41): Over/Under Flow Output. High when an over or under flow has occurred. MODE (Pin 42): Output Format and Clock Duty Cycle Stabilizer Selection Pin. Connecting MODE to 0V selects offset binary output format and turns the clock duty cycle stabilizer off. Connecting MODE to 1/3 VDD selects offset binary output format and turns the clock duty cycle stabilizer on. Connecting MODE to 2/3 VDD selects 2’s complement output format and turns the clock duty cycle stabilizer on. Connecting MODE to VDD selects 2’s complement output format and turns the clock duty cycle stabilizer off. SENSE (Pin 43): Reference Programming Pin. Connecting SENSE to VCM 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 SENSE selects an input range of ±VSENSE. ±1V is the largest valid input range. VCM (Pin 44): 1.6V Output and Input Common Mode Bias. Bypass to ground with 2.2µF ceramic chip capacitor. Exposed Pad (Pin 49): ADC Power Ground. The exposed pad on the bottom of the package needs to be soldered to ground. 22323fa 12 LTC2232/LTC2233 W FUNCTIONAL BLOCK DIAGRA U U AIN+ AIN– VCM INPUT S/H FIRST PIPELINED ADC STAGE THIRD PIPELINED ADC STAGE SECOND PIPELINED ADC STAGE FOURTH PIPELINED ADC STAGE 1.6V REFERENCE 2.2µF SHIFT REGISTER AND CORRECTION RANGE SELECT REFH SENSE FIFTH PIPELINED ADC STAGE REFL INTERNAL CLOCK SIGNALS OVDD REF BUF OF DIFFERENTIAL INPUT LOW JITTER CLOCK DRIVER DIFF REF AMP CONTROL LOGIC • • • OUTPUT DRIVERS D9 D0 CLKOUT REFLB REFHA 2.2µF 0.1µF 22323 F01 REFLA REFHB OGND + ENC – ENC M0DE SHDN OE 0.1µF 1µF 1µF Figure 1. Functional Block Diagram W UW TI I G DIAGRA S Timing Diagram tAP ANALOG INPUT N+4 N+2 N N+3 N+1 tH tL ENC – ENC + tD N–5 D0-D9, OF N–4 N–3 N–2 N–1 tC CLOCKOUT 22323 TD02 22323fa 13 LTC2232/LTC2233 U U W U APPLICATIO S I FOR ATIO DYNAMIC PERFORMANCE 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. 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, 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. Signal-to-Noise Ratio Spurious Free Dynamic Range (SFDR) 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. 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. Signal-to-Noise Plus Distortion Ratio 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: 2 2 2 2 THD = 20Log (√(V2 + V3 + V4 + . . . Vn )/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. Intermodulation Distortion 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. 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. Aperture Delay Time The time from when a rising ENC+ equals the ENC– voltage 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) 22323fa 14 LTC2232/LTC2233 U W U U APPLICATIO S I FOR ATIO CONVERTER OPERATION As shown in Figure 1, the LTC2232/LTC2233 is a CMOS pipelined multistep converter. The converter has five 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 sensitive applications, the analog inputs can be driven single-ended with slightly worse harmonic distortion. The encode input is differential for improved common mode noise immunity. The LTC2232/LTC2233 has two phases of operation, determined by the state of the differential ENC+/ENC– input pins. For brevity, the text will refer to ENC+ greater than ENC– as ENC high and ENC+ less than ENC– as ENC low. 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 ENC 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 ENC transitions from low to high, the sampled input is held. While ENC 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 ENC. When ENC 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 ENC goes back high, the second stage produces its residue which is acquired by the third stage. An identical process is repeated for the third and fourth stages, resulting in a fourth stage residue that is sent to the fifth 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 LTC2232/ LTC2233 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. LTC2232/LTC2233 VDD AIN+ CSAMPLE 1.6pF 15 CPARASITIC 1pF VDD AIN– CSAMPLE 1.6pF 15 CPARASITIC 1pF VDD 1.6V 6k ENC+ ENC– 6k 1.6V 22323 F02 Figure 2. Equivalent Input Circuit 22323fa 15 LTC2232/LTC2233 U W U U APPLICATIO S I FOR ATIO During the sample phase when ENC is low, the transistors connect the analog inputs to the sampling capacitors and they charge to, and track the differential input voltage. When ENC transitions from low to high, the sampled input voltage is held on the sampling capacitors. During the hold phase when ENC is high, the sampling capacitors are disconnected from the input and the held voltage is passed to the ADC core for processing. As ENC transitions from high to low, the inputs are reconnected to the sampling 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 1.6V 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 1.6V. The VCM output pin (Pin 44) 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. the sample-and-hold circuit will connect the 1.6pF sampling capacitor to the input pin and start the sampling period. The sampling period ends when ENC 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 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 LTC2232/LTC2233 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 AIN+ 0.1µF LTC2232/ LTC2233 12pF Input Drive Impedance As with all high performance, high speed ADCs, the dynamic performance of the LTC2232/LTC2233 can be influenced by the input drive circuitry, particularly the second and third harmonics. Source impedance and input reactance can influence SFDR. At the falling edge of ENC, 25Ω 25Ω T1 = MA/COM ETC1-1T RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE AIN– 22323 F03 Figure 3. Single-Ended to Differential Conversion Using a Transformer 22323fa 16 LTC2232/LTC2233 U W U U APPLICATIO S I FOR ATIO 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. 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. 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 higher than 100MHz, the capacitor may need to be decreased to prevent excessive signal loss. For input frequencies above 100MHz 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 1.6V. In Figure 8 the series inductors are impedance matching elements that maximize the ADC bandwidth. Reference Operation Figure 9 shows the LTC2232/LTC2233 reference circuitry consisting of a 1.6V 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; typing the SENSE pin to VCM selects the 1V range. The 1.6V 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 1.6V 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 four pins: two each of REFHA and REFHB for the high reference and two each of REFLA and REFLB for the low reference. The multiple output pins are needed to reduce package inductance. Bypass capacitors must be connected as shown in Figure 9. Other voltage ranges in 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. 22323fa 17 LTC2232/LTC2233 U W U U APPLICATIO S I FOR ATIO VCM VCM 2.2µF HIGH SPEED DIFFERENTIAL 25Ω AMPLIFIER ANALOG INPUT + 2.2µF 10k 0.1µF AIN+ 25Ω ANALOG INPUT LTC2232/ LTC2233 + CM – 10k 12pF – 25Ω AMPLIFIER = LTC6600-20, AD8138, ETC. AIN– 0.1µF 22323 F04 Figure 4. Differential Drive with an Amplifier 25Ω 0.1µF T1 0.1µF AIN+ 2.2µF 0.1µF LTC2232/ LTC2233 25Ω 0.1µF LTC2232/ LTC2233 T1 0.1µF 12Ω T1 = MA/COM ETC1-1-13 RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE AIN+ ANALOG INPUT 8pF 25Ω 22323 F05 VCM 2.2µF 12Ω AIN– Figure 5. Single-Ended Drive VCM ANALOG INPUT LTC2232/ LTC2233 12pF 25Ω 0.1µF AIN+ AIN– 22323 F06 Figure 6. Recommended Front End Circuit for Input Frequencies Between 100MHz and 250MHz 25Ω T1 = MA/COM ETC1-1-13 RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE AIN– 22323 F07 Figure 7. Recommended Front End Circuit for Input Frequencies Between 250MHz and 500MHz 22323fa 18 LTC2232/LTC2233 U W U U APPLICATIO S I FOR ATIO VCM LTC2232/LTC2233 2.2µF 0.1µF AIN+ 4.7nH ANALOG INPUT 25Ω 0.1µF T1 VCM 1.6V 25Ω 1V LTC2232/ LTC2233 4.7nH AIN– T1 = MA/COM ETC1-1-13 RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE INDUCTORS 0603 OR 0402 1.6V BANDGAP REFERENCE 2.2µF 22323 F08 TIE TO VDD FOR 2V RANGE; TIE TO VCM FOR 1V RANGE; RANGE = 2 • VSENSE FOR 0.5V < VSENSE < 1V 1µF 0.5V RANGE DETECT AND CONTROL 2pF 0.1µF 4Ω SENSE REFLB 0.1µF REFHA BUFFER INTERNAL ADC HIGH REFERENCE 2.2µF Figure 8. Recommended Front End Circuit for Input Frequencies Above 500MHz DIFF AMP 1µF REFLA 1.6V 0.1µF VCM REFHB INTERNAL ADC LOW REFERENCE 2.2µF 22323 F09 12k 0.8V 12k SENSE LTC2232/ LTC2233 Figure 9. Equivalent Reference Circuit 1µF 22323 F10 Figure 10. 1.6V Range ADC 22323fa 19 LTC2232/LTC2233 U W U U APPLICATIO S I FOR ATIO Input Range 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 1.5dB. See the Typical Performance Characteristics section. Driving the Encode Inputs The noise performance of the LTC2232/LTC2233 can depend on the encode signal quality as much as on the analog input. The ENC+/ENC– inputs are intended to be driven differentially, primarily for noise immunity from common mode noise sources. Each input is biased through a 6k resistor to a 1.6V bias. The bias resistors set the DC operating point for transformer coupled drive circuits and can set the logic threshold for single-ended drive circuits. Any noise present on the encode signal will result in additional aperture jitter that will be RMS summed with the inherent ADC aperture jitter. LTC2232/LTC2233 VDD TO INTERNAL ADC CIRCUITS VDD 1.6V BIAS 6k ENC+ 0.1µF 1:4 CLOCK INPUT VDD 50Ω 1.6V BIAS 6k ENC– 22323 F11 Figure 11. Transformer Driven ENC+/ENC– In applications where jitter is critical (high input frequencies) take the following into consideration: 1. Differential drive should be used. 2. Use as large an amplitude as possible; if transformer coupled use a higher turns ratio to increase the amplitude. 3. If the ADC is clocked with a sinusoidal signal, filter the encode signal to reduce wideband noise. 4. Balance the capacitance and series resistance at both encode inputs so that any coupled noise will appear at both inputs as common mode noise. The encode inputs have a common mode range of 1.1V to 2.5V. Each input may be driven from ground to VDD for single-ended drive. Maximum and Minimum Encode Rates The maximum encode rate for the LTC2232/LTC2233 is 105Msps (LTC2232) and 80Msps (LTC2233). For the ADC to operate properly, the encode signal should have a 50% (±5%) duty cycle. Each half cycle must have at least 4.5ns (LTC2232) or 5.9ns (LTC2233) for the ADC internal circuitry to have enough settling time for proper operation. Achieving a precise 50% duty cycle is easy with differential sinusoidal drive using a transformer or using symmetric differential logic such as PECL or LVDS. 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 ENC+ pin to sample the analog input. The falling edge of ENC+ is ignored and the internal falling edge is generated by a phase-locked loop. The input clock duty cycle can vary from 20% to 80% 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. 22323fa 20 LTC2232/LTC2233 U W U U APPLICATIO S I FOR ATIO The lower limit of the LTC2232/LTC2233 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 LTC2232/LTC2233 is 1Msps. DIGITAL OUTPUTS Table 1 shows the relationship between the analog input voltage, the digital data bits and the overflow bit. Table 1. Output Codes vs Input Voltage AIN+ – AIN– (2V Range) OF D9 – D0 (Offset Binary) D9 – D0 (2’s Complement) >+1.000000V +0.998047V +0.996094V 1 0 0 11 1111 1111 11 1111 1111 11 1111 1110 01 1111 1111 01 1111 1111 01 1111 1110 +0.001953V 0.000000V –0.001953V –0.003906V 0 0 0 0 10 0000 0001 10 0000 0000 01 1111 1111 01 1111 1110 00 0000 0001 00 0000 0000 11 1111 1111 11 1111 1110 –0.998047V –1.000000V