1 Introduction to Isolated Amplifiers

Figure 1-1 shows the implementation of an isolated-amplifier-based measurement design.

Figure 1-1 Isolated Amplifier Implementation

The input stage of an isolated amplifier consists of an input amplifier that drives a delta-sigma (ΔΣ) modulator. The gain of the input amplifier is fixed and set by internal precision resistors. The ΔΣ modulator uses the internal reference voltage and clock generator to convert the analog input signal to a digital bit stream. The drivers transfer the output of the modulator across an isolation barrier that separates the high and low voltage domains. The received bitstream and clock are synchronized and processed by an analog low-pass filter on the low voltage side and presented as an analog output signal.

The differential output of the isolated amplifier is often converted to a single-ended analog output with an op-amp-based circuit. This op-amp-based circuit can also implement a low-pass filter to further reduce the signal bandwidth to a bandwidth of interest and thereby improve the system noise performance.

The analog-to-digital converter (ADC), either external or internal to the microcontroller (MCU) or digital signal processor (DSP), receives this feedback analog output and converts this output back to the digital domain.