This circuit diagram shows the MC1496 IC in a balanced modulator circuit operating with +12 and –8 volt supplies. Excellent gain and carrier suppression can be obtained with this balanced modulator circuit by operating the upper (carrier) differential amplifiers at a saturated level and the lower differential amplifier in a linear mode. The recommended input signal levels are 60 mV rms for the carrier and 300 mV rms for the maximum modulating signal levels.
The modulating signal must be kept at a level to insure linear operation of lower differential amplifier Q5–Q6. If the signal input level is too high, harmonics of the modulating signal are generated and appear in the output as spurious sidebands of the suppressed carrier. For a maximum modulating signal input of 300 mV rms, the suppression of these spurious sidebands is typically 55 dB at a carrier frequency of 500 kHz.
If the sine wave carrier signal is replaced with a 300 mV peak–to–peak square wave, an additional 15 dB of carrier, second–harmonic suppression is achieved. Good carrier suppression over a wide temperature range requires low dc resistances between pins 1 and 4 and ground. It is recommended that the values of these resistors not be increased significantly higher than the 51 ohms .