If the total impedance presented to the filter is exactly 50 ohm, the attenuator does nothing. But, with errors in termination, say due to input cap of dut, attenuator reduces mismatch for the filter. This maybe a concern for the response of the passive filter's response. Also, it reduces the signals (say kickback) from the adc going back into the filter/signal generator.
DesertFox wrote on Jul 16th, 2015, 12:52pm:Hi,
For generating low distortion single tone for testing ADCs, the "Data Conversion Handbook" suggests using a 6dB attenuator after the BPF/LPF connected to the sinewave generator, as it isolates the ADC from the output of the filter. Can anybody tell me why I would need this, as long as I use a termination resistor of 50ohm at the input of the ADC? I am attaching the figure.
Thanks