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 bit stream proportional to the analog input. When used in conjunction with the AD1556 digital filter/decimator, the industry's highest performance ADC at a bandwidth of 1+ kHz is realized. The continuous-time analog modulator input architecture avoids the need for an external anti-alias filter. The programmable gain front end simplifies system design, extends the dynamic range, and reduces system board area. Low operating power and standby modes makes the AD1555 ideal for remote battery-powered data acquisition systems.