MCU Metamorphosis—Adding Analog Circuits On-Chip (.PDF Download)

July 17, 2018
MCU Metamorphosis—Adding Analog Circuits On-Chip (.PDF Download)

Why didn’t they do this sooner? That’s the question some embedded engineers designing with microcontrollers (MCUs) are asking about the idea of adding analog signal-chain components in MCUs. With today’s sophisticated semiconductor manufacturing methods and special designs, how hard could it be to put a batch of linear circuits right on the same chip with the processor and memory?

Embedded designers of sensing and measuring devices almost always have to use external analog circuits to condition sensor signals before they can be processed. Just a few of the typical signal-conditioning operations include amplification, filtering, noise mitigation, switching, and data conversion. Such circuitry often takes up more space in the final product than the microcontroller chip itself. Today, though, you can get some MCUs with analog circuits on-chip to fit almost any sensing application.

Analog Enhancements

Some MCUs have had on-chip circuits that facilitate analog functions for years. These include an analog-to-digital converter (ADC), comparators, and pulse-width-modulation (PWM) capability. Now more integrated analog components are being incorporated in some MCU products.

One such example is the smart analog combo (SAC) modules from Texas Instruments. Each module consists of a flexible, programmable-gain op amp and a 12-bit digital-to-analog converter (DAC). Internal switches and multiplexers permit the op amp to be configured in multiple ways that may include inverting and non-inverting amplifiers, a follower, or transimpedance amplifier (TIA).

Figure 1 shows the SAC module. The op amp is a single-supply design that requires a bias voltage to center the output within the output voltage range available (2 to 3.6 V). An internal resistive feedback network allows you to select multiple fixed gain settings from 1 to 33. A power-mode selection feature permits a higher gain bandwidth and slew rate if low power consumption is not too much of a problem.


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