Fixed gain amplifier circuit

摘要

An instrumentation amplifier includes first and second resistors for gain setting. The operational amplifiers within the instrumentation amplifier include selectively enabled current drive sources coupled to the amplifier output. The first and second resistors have variable resistances. A control circuit is configured to select the variable resistances of the first and second resistors to implement a fixed gain for the instrumentation amplifier and further selectively enable the current drive sources. The control circuit receives an indication of a downstream programmable gain (for example, from a downstream programmable gain amplifier). The variable resistances of the first and second resistors are selected to be scaled inversely with respect to the downstream programmable gain and the current drive sources are enabled proportionately with respect to the downstream programmable gain.

主权项

1. A circuit, comprising:
a first differential amplifier having an inverting input, a non-inverting input and an output and having a plurality of selectively enabled current drive sources coupled to the output; a first resistor having a first variable resistance coupled between the output and inverting input of the first differential amplifier; a second resistor having a second variable resistance coupled to the inverting input of the first differential amplifier; a control circuit configured to select the first and second variable resistances to implement a fixed gain at the output and further selectively enable the current drive sources, said control circuit receiving an indication of a downstream programmable gain; wherein the first and second variable resistances are selected scaled inversely with respect to the downstream programmable gain; and wherein the current drive sources are enabled proportionately with respect to the downstream programmable gain.