Flying capacitor and negative time constant make digitally programmable-gain instrumentation amplifier - EDN
High Accurancy AD623 Programmable Gain Instrumentation Amplifier CMRR Max 200Hz Digital DC Instrument Amplifier Board Module: Amazon.com: Industrial & Scientific
MAX9939 SPI-Programmable Gain Amplifier (PGA) with Input VOS Trim and Output Op Amp | Maxim Integrated
Programmable Gain Instrumentation Amplifiers: Finding One that Works for You - Embedded Computing Design