Testing a Precision Rectifier Around Zero Crossing

A precision rectifier can produce the expected large-signal output while distorting small signals around zero. That region matters when the circuit feeds a level detector, envelope estimator, or measurement channel. Validate low-amplitude behavior and polarity transitions using the actual amplifier supplies and output load.

Establish the operating range

The TI low-input-voltage full-wave rectifier reference circuit uses a small negative amplifier supply to improve operation near zero. This illustrates that nominal single-supply operation does not automatically provide accurate output all the way to ground.

Record minimum input amplitude, maximum frequency, allowed error, supply rails, and the downstream input range. Include any DC offset that can appear at the rectifier input.

Measure the crossing directly

Capture input and output together and expand the time and voltage scales around each zero crossing. Compare the measured output with the intended absolute-value transfer, including the circuit’s gain.

Look for dead regions, delayed recovery, overshoot, and different behavior for the two input polarities. An output plot scaled to show the largest peak can hide an error that dominates the smallest useful signal.

Sweep amplitude and frequency separately

Start with a low frequency and reduce amplitude through the required range. Then increase frequency at several fixed amplitudes. This separates low-level offset and headroom issues from speed-related behavior.

For example, a circuit used to measure a small residual signal may need its error stated in millivolts rather than only as a percentage of the largest input. Define the metric before comparing alternative amplifiers or diode arrangements.

Check the complete output path

Connect the intended filter, ADC input, or load. Measure whether it changes the rectifier’s near-zero behavior. A capacitive load or sampling input may create a different transient response from a high-impedance oscilloscope alone.

Observe relevant amplifier outputs inside the circuit where access permits. A stage that reaches a limiting condition during one polarity may need time to recover even when the final output appears bounded.

Repeat at supply and temperature conditions that reduce headroom or increase offset. If a negative bias supply is used, include its startup and shutdown behavior in the system check.

Save transfer-error plots, crossing captures, load conditions, and the smallest signal that meets the requirement. The resulting specification should describe usable amplitude and frequency together. A clean rectified waveform at a convenient large input does not establish accurate operation near zero, where amplifier limitations and offsets can consume most of the intended measurement range.