AD633 overmodulation

[oxyde26]

hi,

i use AD633 to make amplitude modulation. i have to show the output signal when modulation index m<1 , m=1 and m>1. however ,i cant see the overmodulation (m>1) output. i used the basic am circuit that shown in datasheet. thanx.

 

[crutschow]

What signals are you applying to the AD633 to generate the m>1 AM signal?

 

[oxyde26]

i applied various sinusoids. for example 1Vpp carrier with message signals 0.5Vpp, 1Vpp, up to 10Vpp.

 

[crutschow]

If you apply AC signals with no DC bias into a DC coupled multiplier then you will achieve double-sideband suppressed-carrier modulation. Is that what you want?

If you want normal amplitude modulation then you need to add a DC bias voltage to the modulation signal. That way you get a carrier output with no AC modulation if the AC modulation signal is zero, as required. For example a modulation signal with a 1Vdc bias and a 0.5Vpp AC component will give 50% modulation to the carrier input.