The AD1555 is a complete sigma-delta modulator， combined with a programmable gain amplifier intended for low frequency， high dynamic range measurement applications. The AD1555 outputs a ones-density bitstream proportional to the analog input. When used in conjunction with the AD1556 digital filter/ decimator， a high performance ADC is realized. The continuous-time analog modulator input architecture avoids the need for an external antialias filter. The programmable gain front end simplifies system design， extends the dynamic range， and reduces the system board area. Low operating power and standby modes makes the AD1555 ideal for remote battery-powered data acquisition systems. The AD1555 is fabricated on Analog Devices’ BiCMOS process that has high performance bipolar devices along with CMOS transistors. The AD1555 and AD1556 are packaged， respectively， in 28-lead PLCC and 44-lead MQFP packages and are specified from –55°C to +85°C （AD1556 and AD1555 B Grade） and from 0°C to 85°C （AD1555 A Grade）.