Digital Signal Processing Reference
In-Depth Information
spaced from the carrier at an offset of the modulation frequency. More-
over, sub-harmonics at an offset of the carrier frequency are produced. The
latter have to be suppressed by means of a lowpass filter.
Fig.13.2.
Mixer and mixing process. Amplitude modulation with suppressed car-
rier
LO
RF
IF
Fig. 13.3.
Block diagram of a double-balanced mixer
Fig. 13.3. is a block diagram of a modern analog double-balanced
mixer. The polarity of the modulation signal is switched by 4 PIN diodes.
The carrier signal (LO = local oscillator) is coupled in via an RF trans-
former, and the modulation product is coupled out via an RF transformer.
The modulation signal is fed DC-coupled.
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