Datasheet AD1555, AD1556 (Analog Devices)

a
24-Bit - ADC with Low Noise PGA AD1555/AD1556 FEATURES
high dynamic range measurement applications. The AD1555
AD1555
outputs a ones-density bitstream proportional to the analog
Fourth Order - Modulator
input. When used in conjunction with the AD1556 digital filter/
Large Dynamic Range
decimator, a high performance ADC is realized.
116 dB Min, 120 dB Typical @ 1 ms
The continuous-time analog modulator input architecture avoids
117 dB Typical @ 0.5 ms
the need for an external antialias filter. The programmable gain
Low Input Noise: 80 nV rms @ 4 ms with
front end simplifies system design, extends the dynamic range,
Gain of 34,128
and reduces the system board area. Low operating power and
Low Distortion: –111 dB Max, –120 dB Typical
standby modes makes the AD1555 ideal for remote battery-pow-
Low Intermodulation: 122 dB
ered data acquisition systems.
Sampling Rate at 256 kSPS Very High Jitter Tolerance
The AD1555 is fabricated on Analog Devices’ BiCMOS process
No External Antialias Filter Required
that has high performance bipolar devices along with CMOS
Programmable Gain Front End
transistors. The AD1555 and AD1556 are packaged, respectively,
Input Range: 2.25 V
in 28-lead PLCC and 44-lead MQFP packages and are specified
Robust Inputs
from –55°C to +85°C (AD1556 and AD1555 B Grade) and from
Gain Settings: 1, 2.5, 8.5, 34, 128
0°C to 85°C (AD1555 A Grade).
Common-Mode Rejection (DC to 1 kHz) 0 93 dB Min, 101 dB Typical @ Gain of 1 fIN = 24.4Hz 77 mW Typical Low Power Dissipation –20 SNR = 116.7dB Standby Modes THD = –120.6dB –40 AD1556 FIR Digital Filter/Decimator –60 Serial or Parallel Selection of Configuration –80 Output Word Rates: 250 SPS to 16 kSPS –100 6.2 mW Typ Low Power Dissipation 70 W in Standby Mode –120 AMPLITUDE – dBr Reference Design and Evaluation Board with –140 Software Available –160 APPLICATIONS –180 Seismic Data Acquisition Systems –200 Chromatography 0 50 100 150 200 250 300 350 400 450 500 Automatic Test Equipment FREQUENCY – Hz
Figure 1. FFT Plot, Full-Scale AIN Input, Gain of 1
GENERAL DESCRIPTION
The AD1555 is a complete sigma-delta modulator, combined with a programmable gain amplifier intended for low frequency,
FUNCTIONAL BLOCK DIAGRAM REFIN REFCAP2 REFCAP1 AGND3 PGA0...PGA4 H/S ERROR CB0...CB4 MODE CONTROL PGA CONFIGURATION INPUT SHIFT DIN REF DIVIDER LOGIC CONTROL REGISTER REGISTER SCLK MFLG OVERVOLTAGE DAC STATUS CS DETECTION REGISTER R/W CSEL DATA PGA INPUT DIGITAL LOOP TDATA OUTPUT DOUT MUX FILTER FILTER MUX AIN (+) MUX MDATA DRDY AIN (–) DATA CLOCK TIN (+) REGISTER RSEL CLOCK DIVIDER GENERATION TIN (–) AD1555 MCLK AD1556 AGND1 PGAOUT MODIN AGND2 +V –V V DGND A A L CLKIN SYNC BW0...BW2 RESET PWRDN GND VL
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