Integrating Moving Average Filter Windows with Analog Converter Downsampling Rates
Aligning moving average filter lengths as integer multiples of ADC decimation rates eliminates aliasing foldover and maximizes noise bandwidth reduction.
Power Line Rejection
Noise Attenuation
A performance parameter quantifies the ability of an electronic circuit to suppress unwanted signals originating from the AC mains power grid. This power line rejection is critical for maintaining high resolution in sensitive analog and sensor systems. The measurement is usually expressed in decibels at the specific line frequencies of fifty or sixty hertz.
High rejection ensures that mains hum does not corrupt the output signal.
Circuit Design
Differential amplifiers and active filters are configured to provide high common mode rejection at the power line frequencies. Selecting components with tight tolerances prevents mismatch and maintains balanced signal paths. Proper decoupling of power rails also helps prevent mains noise from entering the signal path.
Measurement Method
Evaluation involves injecting a known AC disturbance onto the power supply line and measuring the resulting signal level at the circuit output. Signal generators and spectrum analyzers are used to perform this test across the frequency band. The ratio of the injected input noise to the output noise determines the rejection factor.
Shielded test environments are required to prevent external electromagnetic interference from affecting the test results.
Layout Practice
Proper grounding and shielding of sensitive signal traces reduces the inductive coupling of mains noise. Keeping AC power routing physically separated from analog circuits prevents the transfer of electromagnetic interference. These design rules are essential for achieving the calculated rejection levels.