Frequency converter for quadrature modulator or demodulator - using heterodyne signal generator providing quadrature signals with 90 degree phase-shift

摘要

The frequency converter for a quadrature modulator or demodulator uses a heterodyne signal generator (TG). An associated regulating circuit stabilises the 90 degrees phase shift between the 2 quadrature heterodyne signals (TI,TQ). Pref. the heterodyne signal generator (TG) contains an amplifier, controlled by an oscillator signal (LO), a further regulating circuit containing a symmetry detector for the pulse ratio of the amplifier output signals, for maintaining a pulse ratio of 0.5. A quadrature phase divider pref. uses a frequency doubler and a master slave flip-flop in series, the outputs of the master stage and the slave stage providing here 2 quadrature signals (TI,TQ).