24-Bit - ADC a 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 The AD1555 is fabricated on Analog Devices BiCMOS process Very High Jitter Tolerance that has high performance bipolar devices along with CMOS No External Antialias Filter Required 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 55C to +85C (AD1556 and AD1555 B Grade) and from Gain Settings: 1, 2.5, 8.5, 34, 128 0C to 85C (AD1555 A Grade). Common-Mode Rejection (DC to 1 kHz) 0 93 dB Min, 101 dB Typical Gain of 1 f = 24.4Hz IN 20 77 mW Typical Low Power Dissipation SNR = 116.7dB THD = 120.6dB Standby Modes 40 AD1556 60 FIR Digital Filter/Decimator 80 Serial or Parallel Selection of Configuration Output Word Rates: 250 SPS to 16 kSPS 100 6.2 mW Typ Low Power Dissipation 120 70 W in Standby Mode 140 Reference Design and Evaluation Board with Software Available 160 APPLICATIONS 180 Seismic Data Acquisition Systems 200 Chromatography 0 50 100 150 200 250 300 350 400 450 500 FREQUENCY Hz Automatic Test Equipment 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 LOGIC CONTROL REGISTER REGISTER REF DIVIDER SCLK MFLG OVERVOLTAGE STATUS CS DAC DETECTION REGISTER R/W CSEL DATA DIGITAL PGA INPUT TDATA OUTPUT DOUT LOOP MUX FILTER MUX FILTER MUX AIN (+) DRDY MDATA AIN () DATA REGISTER CLOCK RSEL TIN (+) CLOCK DIVIDER GENERATION MCLK AD1555 TIN () AD1556 AGND1 PGAOUT MODIN AGND2 +V V V DGND CLKIN SYNC BW0...BW2 RESET PWRDN GND V A A L L REV. B Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. use, nor for any infringements of patents or other rights of third parties that Tel: 781/329-4700 www.analog.com may result from its use. No license is granted by implication or otherwise Fax: 781/326-8703 Analog Devices, Inc., 2002 under any patent or patent rights of Analog Devices. AMPLITUDE dBrAD1555/AD1556 (+V = +5 V V = 5 V V = 5 V AGND = DGND = 0 V MCLK = 256 kHz T = T to A A L A MIN T , unless otherwise noted.) AD1555SPECIFICATIONS MAX AD1555BP AD1555AP Parameter Notes Min Typ Max Min Typ Max Unit PGA Gain Settings 1, 2.5, 8.5, 34, 128 AC ACCURACY 1 Dynamic Range PGA Gain of 1 116.5 120 116 120 dB PGA Gain of 2.5 116 119.5 115.5 119.5 dB PGA Gain of 8.5 114 117.5 114 117.5 dB PGA Gain of 34 104.5 109.5 104.5 109.5 dB PGA Gain of 128 98 98 dB 2 Total Harmonic Distortion PGA Gain of 1 120 111 120 107 dB PGA Gain of 2.5 116 108 116 107 dB PGA Gain of 8.5 116 106 116 105 dB PGA Gain of 34 115 101 115 101 dB PGA Gain of 128 108 108 dB 3 Jitter Tolerance 300 300 ps 4 Intermodulation Distortion PGA Gain of 1 122 122 dB DC ACCURACY 5 Absolute Gain Error PGA Gain of 1, 2.5 3.5 +3.5 3.5 +3.5 % PGA Gain of 8.5 4.5 +4.5 4.5 +4.5 % PGA Gain of 34 10 +10 10 +10 % 5 Gain Stability Over Temperature 15 15 ppm/C 5, 6 Offset All PGA Gain 60 60 mV 5, 6 Offset Drift 66 V/C ANALOG INPUT Full-Scale Nondifferential Input MODIN 2.25 2.25 V Input Impedance MODIN 20 20 k Full-Scale Differential Input PGA Gain of 1 2.25 2.25 V Other PGA Gain Settings See Table I See Table I Differential Input Impedance AIN, TIN Inputs 140 140 M Common-Mode Range 2.25 2.25 V Common-Mode Rejection Ratio V = 2.25 V, f = 200 Hz CM IN PGA Gain of 1 93 101 91 101 dB PGA Gain of 2.5 95 102 91.5 102 dB PGA Gain of 8.5, 34 95.5 108 94.5 108 dB PGA Gain of 128 108 108 dB 7 Power Supply Rejection Ratio 50 50 dB AIN to TIN Crosstalk Isolation f = 200 Hz 130 130 dB IN Differential Input Current 130 130 nA 8 TEMPERATURE RANGE Specified Performance T to T 55 +85 0 85 C MIN MAX 9 REFERENCE INPUT Input Voltage Range 2.990 3.0 3.010 2.990 3.0 3.010 V Input Current 130 130 A DIGITAL INPUTS OUTPUTS V 0.3 +0.8 0.3 +0.8 V IL V 2.0 V + 0.3 2.0 V + 0.3 V IH L L I 10 +10 10 +10 A IL I 10 +10 10 +10 A IH V I = +2 mA 0.4 0.4 V OL SINK V I = 2 mA 2.4 2.4 V OH SOURCE 2 REV. B