I would like to use the MPY634 as a AM modulator. The circuit is wired exactly as mentioned in the datasheet figure 9 page 8.
Modulation input Em is + - 5V @ 150 Hz (square wave); Carrier input Ec= + - 8V @ 2 Khz (square wave) ; Power supply is + - 15V DC.
SF pin is left open.
Problem:
When Em is 0; and Ec is + -8V @ 2KHz; The output is same as the input (Ec) as expected and clean and symmetrical.
Now when Em is slowly increased to + -1V / sq wave ; the output is AM modulated wave; but there is asymmetry in the waveform with the negative peak at ~-13 V pk and positive peak at ~+9 V pk.
Also the depth of modulation is unequal across the x axis.
Addition to this, there is a waveform distortion at the output.
Query:
1) Any help on what could be the issue?
2) What is the role of the SF pin? The datasheet is not very clear on this.
3) How to smoothly vary the Em signal and obtain a nice AM moduated waveform without distortion?
Thanks in advance for the help.