How to find the right Differential Amplifiers AI guide
Written by an AI model from its trained knowledge.
What the AI looks for in Differential Amplifiers
- Common-mode rejection (CMRR)
- Compare CMRR at your signal frequency, not only at DC. Integrated laser-trimmed resistor parts beat discrete-resistor builds. Rejecting noise common to both inputs is the whole point of a differential amplifier, and mismatched resistors destroy it.
- Difference vs instrumentation vs fully differential
- Use a difference amp for high common-mode voltages such as current shunts, an instrumentation amp for high-impedance sensors such as bridges and thermocouples, and a fully differential amp to drive differential ADC inputs. These three types solve different problems despite the shared name.
- Input common-mode range
- The input common-mode voltage plus the signal must stay within the datasheet range at your supply voltage. Exceeding it saturates the output even though the differential signal is small.
- Gain setting
- Use fixed-gain parts for repeatability. Choose a single-resistor-gain instrumentation amp if you need adjustable gain. The gain resistor's tolerance and temperature drift go straight into your measurement error.
- Supply and output swing
- For 3.3 V or 5 V single-supply systems, choose parts rated for single-supply operation with rail-to-rail output. Older dual-supply parts can't swing near ground on a single supply.
Brands that matter
- Texas Instruments: Makes the INA-series difference, current-sense and instrumentation amplifiers.
- Analog Devices: Makes the AD62x instrumentation and AD82xx difference amplifier families.
- Microchip: Makes low-voltage instrumentation and current-sense amplifiers.
- Adafruit: Sells breakouts that put common sense/instrumentation amp chips on breadboard-friendly boards.
What to avoid
- Building a difference amp from a general op-amp and 1% resistors when you need high CMRR.
- Choosing a difference amp for high-impedance sensors, because its input resistors load the source.
- Ignoring the input common-mode limit on high-side current sensing.
Questions
What is the difference between a difference amplifier and an instrumentation amplifier?
A difference amp uses internal resistors and can handle large common-mode voltages but has low input impedance. An instrumentation amp has buffered high-impedance inputs and adjustable gain, which suits sensors.