We have:

ADC2 Left Input 1=2.25V +small AC signal

Differential mode setting and gain=1.

The Data sheet says

Full-Scale Input Voltage (Differential) 2.18V ( RMS), 24 bit ADC

My question is :

(1)  If differential input voltage= -0.1V, what is the ADC2 digital output? Is ADC2 unipolar or bipolar?

(2) If differential input voltage=0.1V, what is the ADC2 digital output?

(3) if the differential input voltage is constant DC voltage, then will the ADC 2 output  be zero?

we would like understand, verify and test how CODEC ADC works.

Thanks

• Hello blackfin,

These are audio specific ADCs where the 7714 is designed for data conversion so there are other options. The 1836A's ADCs are sitting up at a common mode input DC level. The ADC will produce a 2's compliment 24 bit output. So if the input of the ADC is sitting at the 2.5V common mode, it will produce a zero output. (now this is ideal, in reality there is always a DC offset since no converter is perfect.). So 2.5V will produce zero. A slight positive DC signal above 2.5V will produce a positive number. The max is 0x7FFFFF. Note the sign bit is low.

For a slightly negative number, just one bit negative will produce 0xFFFFFF which is a minus 0x000001 in 2's compliment form. So the maximum negative number possible is 0x800000. Note the sign but is high.

So if the input is a constant DC offset then it will output a constant number. It can be a positive or negative number depending on the DC voltage as it compares to the common mode voltage of ~2.5V.

Dave T

The datasheet says

" Full-Scale Input Voltage (Differential) 2.18 (rms) -----------6.16V (V pp)"

"Vref=2.25V ( common mode)"

in our differential mode design,  assuming Gain=1, when the differential input voltage is   3.08V,  ADC output will be saturated to the most positive-MAX number , and when the differential input voltage is    -3.08V,  ADC output will be saturated to most negative- MIN number?

Thanks

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Thank you,