We use AD9245 to sample the signal detect single end amplifier with output voltage from 0 to 2 volts. We connect this output to Vin+. My question is that should we connect the Vin- to ground or to a voltage reference of 1 volt. If we connect the Vin- to ground, the differential input of AD9245 will be from 0 to 2 volts. If we connect the Vin- to 1 volt reference, the differential input of AD9245 will be from -1 to 1 volt. Could you please tell us which solution is right or both are right?
For a 2 V input single-ended input span ranging from 0 to +2 V, the VREF output must be configured for 1 V while the VIN- pin is connected to VREF via the same value resistor (i.e. 33 ohms) that is used to connect VIN+ to the amplifier source which is producing the 0 to 2 V input signal.
we follow this setting, and 1V give VIN- to have 0-2V input as ±1V digital output for servo control.
target is to match VIN+=VIN- as 1V.
by now we get +60mV different between VIN+ with VIN- when servo is working(VIN+ always bigger than VIN-).
is that means the VIN+ reading is 6% less than real voltage?
if I change target half, I will have +30mV VIN+ bigger than VIN-.
because the code only check AD9245 is 0 or not, reduce output when bigger than 0 and increase output when less than 0.
both VIN+ and VIN- has 33 ohms input resistor.
VREF connect to VIN-, there is 1K to ground before 33 ohm.
input through 33 ohm to VIN+, no resistor between it with ground.
could you please help check if any connection worn?
If you run AD9245 at 1V internal reference by connecting SENSE pint to ground and bias VIN- with 1V VREF, you shouldn't need 1K ohm to ground on VIN- side. The source impedance on each inputs should be well matched in order to achieve the best possible performance.
Questions are : When you say " change target half", what does that mean? Does it mean to set VIN+=0.5V = 1/2 VIN- ?
How do you set the output common mode voltage on AMP output(=VIN+ of AD9245)?
The digital code "0" covers within +/- 1/2 LSB (61uV here) and offset error of AD9245 on datasheet is typically +/-0.3% and Max +/-1.2% FSR @ 1.0V internal reference. Offset error at Max 1.2% case is 2V_FS*1.2*0.01=24mV. So it doesn't explain 60mV fully here. Please let me know if there is any change without 1K ohm on VIN- side.