Logarithmic converter for input circuit of waveform analyser e.g. spectrum analyser

摘要

The converter has an intermediate frequency section (IF) with switches (106,107) used to select between the outputs of two bandpass filters (102,105) with different centre frequencies. A mixer, whose output is fed to the second bandpass filter, combines the output of a local oscillator (104) and the first bandpass filter. A logarithmic conversion section (LOG) has two logarithmic conversion amplifiers (108,111). A bandpass filter (109) and a low-pass filter (110), connected in parallel, are provided between the two amplifiers and used to suppress noise in the input signal.