The PGA849 is a monolithic, high-voltage, precision programmable-gain instrumentation amplifier. The PGA849 combines a high-speed current-feedback input stage with an internally matched gain resistor network, followed by a four-resistor, difference amplifier output stage. Eight pre-programmed binary gains are selectable using gain-select pins A0, A1, A2. Gains range from 0.125V/V to 16V/V, discussed in greater detail in Section 7.3.1.

A functional block diagram for the PGA849 is shown in the next section. The differential input voltage is fed into a pair of matched, high-impedance input, current-feedback amplifiers. An integrated precision-matched gain resistor network is used to amplify the differential input voltage. An output difference amplifier, A₃, rejects the input common-mode component and refers the output signal to the voltage level set by the REF pin.

The PGA849 output amplifier bandwidth is optimized to drive high-performance analog-to-digital converters (ADCs) with sampling rates up to 1MSPS, without the need for an additional ADC driver. The output amplifier uses a separate power supply that is independent of the input-stage power supply. When driving an ADC, use a low-impedance connection from LVDD and LVSS to the ADC power supplies. This configuration protects the ADC inputs from damage due to inadvertent overvoltage conditions.