Patent ID: 7251284

Claim:
A QAM receiver comprising: (a) a signal input for receiving an analog input signal; (b) an anti-aliasing filter and a series connected analog/digital converter for converting the received analog input signal into a digital signal; (c) a carrier frequency loop for detecting a carrier frequency of the received analog input signal; (d) a clock phase loop for detecting a clock phase of the received analog input signal; and (e) a control circuit which is switchable between a receive mode of operation and a test mode of operation, wherein, in the test mode of operation, the control circuit applies a center frequency adjusting signal to the carrier frequency loop for adjustment of a center frequency and applies a frequency band adjusting signal to the clock phase loop for adjustment of a frequency bandwidth to measure power level values for the entire frequency band of the received analog input signal; (f) wherein, in the test mode, a signal output by a signal generator is supplied to the signal input, and an evaluating circuit compares the output signal of the signal generator with an output signal calculated from the measured power level values to determine whether the anti-aliasing filter and the series connected analog/digital converter are operating faultlessly.