FM Detector using a phase shift network and an analog multiplier

In an FM detector comprising:

• (1) a phase shift network for obtaining a phase shift signal whose phase is shifted from that of an FM intermediate frequency signal, and
• (2) an analog multiplier for obtaining an FM detect output signal by detecting a difference between the phases of said FM intermediate frequency signal and said phase shift signal, said analog multiplier including a differential amplifier circuit and a phase detector circuit, said differential amplifier circuit including first and second transistors, the emitters of which are connected in a differential configuration, and at least one of the bases which is driven by said FM intermediate frequency signal, at least said phase shift signal being applied to said phase detector circuit,
• the improvement comprising:
• (1) a third transistor, the base and the emitter of which are respectively connected to the base and the emitter of said first transistor,
• (2) a fourth transistor, the emitter of which is connected to said bases of said first transistor and said third transistor, and
• (3) wherein one of a collector output of said first transistor and a collector output of said fourth transistor is applied to said phase detector circuit, while the other is applied to said phase detector circuit through said phase shift network.