Voltage Measurement Designs For Mixed Signal Electronics

Created: December 1, 2025

Voltage measurements encompass a large range of possible techniques and measurement ranges, from high-voltage DC to low-voltage, high-frequency analog signals. Typically, we are monitoring either a voltage rail or the voltage passed to a load, which is then monitored by comparing with some reference voltage.

This article outlines the common approaches to implementing these voltage measurements with a focus on precision, protection of the circuit, and handling higher voltages. Approaches include using dividers and transformers, passing a signal to an amplifier, or implementing measurement and logic in a mixed-signal processor.

Simplest Approach: Voltage Divider and an Amplifier

A resistor divider is often the starting point for voltage monitoring as it is a simple circuit that scales a higher input voltage down to a range compatible with an ADC, comparator, or amplifier. All divider circuits used as part of voltage measurements must follow some basic rules:

Choose resistor values R1, R2 so that the measured voltage is stepped down to the target range. For moderate voltages, large resistors would be needed to ensure low current is passed through the divider.
The divider’s output must feed a high-impedance input (e.g., ADC, comparator) with the appropriate voltage withstand value so that quiescent current is minimized.
Once the current and input voltages on the divider are known, check the power dissipation in the divider network to ensure the resistors are properly derated.

Both requirements are necessary to avoid loading down a power rail, voltage source, or load that is receiving power.

If the source signal is noisy or there are fast transients (e.g., switching-power rails), consider placing an RC filter (for large load impedances) or a pi filter (for smaller load impedances) to dampen noise before feeding into an ADC, comparator, or amplifier. This also helps stabilize the reading under conditions where the voltage may fluctuate quickly over time.

For high voltage measurements which would be too large for a resistor divider network, the input voltage needs to be stepped down with a transformer and given to the amplifier for measurement. When this is done, the high-impedance input on the amplifier or buffer will not draw much current, so the transformer does not require high power handling capability.

ADCs and Comparators

The above measurement methods provide an analog output, which does not have any usage in digital processing. This needs to be converted to a digital signal so that it can be used in an embedded digital application; this is done in two ways:

Threshold-based measurement with a comparator (or window comparator)
Precision measurement with an ADC

The comparator output essentially gives an output which converges to the required logic level when the voltage is above some reference voltage value. This would be used in applications such as alarms, overvoltage detection, or generating a conditional trigger. Precision measurements which require an exact voltage value rely on an ADC, which then outputs the voltage to a system host over a serial interface (I2C or SPI).

In both cases, the voltage needs to be measured against its own reference net, i.e., the ADC and the voltage to be measured need to share the same ground net on the PCB. This is required to ensure the measured voltage does not have an unintended offset due to ground potential differences, which can arise in electrically isolated systems.

Circuit Protection

Voltage measurement circuits can experience surges in the input voltage, which could destroy the circuit and lead to failure of a device. This is why we would apply some circuit protection on the voltage measurement circuit. The exact approach depends on the expected worst-case voltage surge/transient one would expect; some options are outlined below.

Protection Technique	Purpose	Key Guideline
TVS diode	Clamp transient over-voltage or surges	Use a TVS rated just above normal signal range, with clamp voltage below the max rating of the input.
Series resistor	Limit fault or surge current into sensitive inputs	Typical values: 100-1k Ohms depending on source impedance and acceptable signal droop.
Clamp diodes (Schottky or Zener)	Prevent input voltage from exceeding safe rails	Place diodes to ground and/or supply so input is clamped within safe range under over-voltage.
Galvanic isolation barrier	Separate measurement domain from high-voltage/noisy domains	Use isolation amplifiers or isolated ADC when measuring floating loads or where load and host ground domains differ.
Charge pump-based surge protection	Clamp surge voltage at values typically above what is capable with clamp diodes	Involves MOSFET arrays in parallel, which switches off as a surge passes a set threshold.

So You’ve Measured Voltage… Now What?

Once voltage is being continuously monitored or if a comparative measurement is performed, what can you do with this information? Normally, the output from your measurement circuit will be passed to your system host. The intention would be to perform any of the following functions:

Averaging of measurements over time (in continuous monitoring)
Filtering of the output from your measurement circuit (removing noise)
Applying logical conditions to the output (threshold or window-based measurements)

The first two tasks are either analog or digital signal conditioning and cleanup tasks; Option 1 is a digital approach where an average is computed in an application, and Option 2 is an analog approach applied before a direct measurement of the circuit output. Option 3 would be applied in the embedded application or on the voltage measurement ASIC itself.

Modern mixed-signal processors allow a designer to build a custom AFE that integrates ADCs, custom logic, and programmable threshold detection with comparators. This provides continuous monitoring, threshold-based alerts, and logic functions applied to comparator outputs. These devices allow you to combine divider/attenuation, analog sensing, and digital logic in one device.

With Renesas GreenPAK, designers can build a fully custom voltage measurement ASIC from an off-the-shelf component with CPLD-like functionality. To accomplish this, Renesas provides the Go Configure Software Hub for configuring programmable logic cells, customizing the component pinout, and designing a fully-integrated analog front-end.

To learn more, take a look at the GreenPAK components and reference examples.

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