| 摘要 |
<p>A frequency difference detector (FDD) implemented as a balanced quadricorrelator has an automatic gain control system (68) having inputs capacitively coupled to the quadrature related, baseband frequency paths from the front end mixers (12,14). The a.g.c. system (68) has quadrature related mixers (78,80) coupled to said inputs for frequency up-converting the baseband signals to an intermediate frequency. The IF signals from the mixers are summed in a summing circuit (82) and subsequently squared in a squaring circuit (86). Any ripple in the output of the squaring circuit is removed by low pass filtering to produce a d.c. control signal which is applied to gain controlled amplifiers (22,24) present in said baseband frequency paths in order to render the output (Vo) of the FDD less sensitive to variations in the input signal (Vi).</p> |
