Hello,
I'm using an AD734 as a lock in amplifier following the schematic on page 12 of the datasheet 'Figure 24. Basic Multiplier Circuit'.
X1 is a sine wave 1Vpp centered at 0V from the signal generator.
X2 is connected to Ground.
Y1 is a square wave 4Vpp centered at 0V from the signal generator.
Y2 is connected to Ground.
Both X1 and Y1 have a frequency of 400KHz.
Z2 is connected to Ground.
The denominator U is set to 1V as described in table 5 page 12 of the datasheet.
I measure the average DC output W with a multimeter (Keithley 2700).
When X1 and Y1 are in phase I get a 0.588V but when I switch the phase of Y1 to 180deg I get -0.580V (8mV difference).
When I set either X1 or Y1 or both to 0Vdc the output at W goes to 0.3mV which is fine.
When the sine wave at X1 is 0.5Vpp the voltage difference goes to 6mV.
For what is my knowledge any DC offset at the input should go to zero in the multiplication process.
I also checked the signal generator and verified the waves are exactly in phase and 180 deg out of phase.
I then do not understand where this 8mV offset may come from.
Any help is appreciated.