When an analogue circuit like an audio IC or an ADC for instance is implemented, is there a dedicated instrument/device which measure the input output impedance of the circuit or one has to perform his own setup?
I am very curios how are such tests are performed and cannot find any information in literature. I basically wonder what professionals use in testing their prototypes besides oscilloscopes and function generators.
For measuring output impedance, one invariably measures the output level while changing the load on the output.
For measuring the input impedance, a common technique is to use a controllable output impedance to drive the device, usually a voltage source with a series resistor, and monitor the output while the resistor is varied.
For 50 Ω RF devices, a network analyser is often used to measure S11 and S22.
For other devices, the variety of frequencies, waveforms, loads, voltages, means that any instrument dedicated to this task would be uneconomic, either addressing a very small section of the market, or having to be hopelessly comprehensive.
In many circuits, the actual "amplification" will have much higher Rin than the spec'd Rin, with the spec being set by a lumped/discrete resistor to Ground.
Given FETs are capacitors (0.001pF on_silicon to 10,000pF?? Power MOSFET), and bipolars will have massive variation in BETA what with manufacturing temperature_annealing variations that vary the base_width, if your system (or your customers' systems work best with a controlled Rin, then you'll not expect the circuit/amplifier to provide the Rin, but will use a lumped/discrete resistor.
