Output Referred Noise

Gain Cascade

Amplifying input signals multiplies input voltage noise by total stage gain while adding internal operational amplifier noise. High closed-loop gain increases output-referred noise levels proportionally to total voltage gain. Downstream active filter stages contribute noise that adds directly to output terminals without gain multiplication.

Total output noise voltage equals the square root of integrated output noise spectral density.

Chain Design

Multi-stage instrumentation amplifiers amplify weak transducer signals to standardized zero-to-ten volt output levels. Managing output referred noise requires balancing stage gain distribution to keep total output noise within analog-to-digital converter input specifications. Cascading low-noise front-end stages with band-limiting filters maintains output noise below digitizer LSB levels.

High output noise floors mask small target signals, lowering effective measurement resolution. Proper decoupling of power supply rails prevents high-frequency rail ripple from reaching output terminals. Shielded cable driver stages prevent output noise degradation over long transmission lines.

Dynamic Boundary

Wideband RMS voltmeters connected directly to output terminals verify noise performance under zero-input conditions. Uncompensated high frequency peaking increases output noise voltage beyond calculated nominal design figures. Elevated ambient operating temperature increases output noise through elevated transistor thermal currents.

Output driver loading reduces open-loop gain, altering internal noise contribution ratios.