Search FAQs on the left to see if your question has been answered. Click on the dropdown to view all of the documents associated with the product. If you can't find your question, click on Ask a Question

AD7790: Shift signals

Sensor output is amplified so that signal lies between -3 and +3 V. System
voltage is 3 V, -3V available from a voltage converter.
Is it possible in some way to use the AD7790 as ADC in that case? What other
possibilities are there to convert the -3 to +3 V signal? Need a low-power
solution.

 

1. Use a Low-power op amp to shift and attenuate the input signal so that the
+/-3V signal range becomes a 1.5V +/-1.5V signal range.
Power the AD7790 from +3V supply (converter GND connected to system ground) and
use the AD7790 in unbuffered mode which gives a rail to rail input swing.
Disadvantages
=> external op amp adds power and noise.


You can also achieve a similar effect by simply using an external resistor
network (see our AD7707 and AD7732) to attenuate  and level-shift the signal so
that it will fit into the ADCs input range when the ADC is powered from 0 to
+3V supplies.

2. Power the AD7790 from the +/-3V supplies (and level shift the digital
control signals so that they are referred to -3V instead of ground.
Then you can drive the AD7790 directly with a +/-3V signal and supply the
AD7790 with a +/-3V reference (if the supply is ow enough noise)
Otherwise you can attenuate the input signal to e.g. +/-2.5V which gives you
the possibility of supplying the reference from +/-2.5V voltge reference ICs.
And then use the converter in buffered mode (to get around the added input
impedance from the resistive divider.
Comments
Anonymous
Related