# AD7765 DiffAmp max input signal

I am about to use AD7765 and i am confused with max input signal level for differential amp.

The datasheet on page 18 says :

The common-mode input at each of the differential amplifier inputs (Pin VINA+ and Pin VINA−) can range from−0.5 V dc to

2.2 V dc. The amplifier has a constant output common-mode voltage of 2.048 V, that is, VREF/2, the requisite common-mode voltage for the modulator input pins (VIN+ and VIN−).

but next paragraph says:

Figure 30 shows the signal conditioning that occurs using the differential amplifier configuration detailed in Table 7 with a

±2.5 V input signal to the differential amplifier. The amplifier in this example is biased around ground and is scaled to give

±3.168 V p-p (−0.5 dBFS) on each modulator input with a 2.048 V common mode.

and follows nice picture with signal +-2.5V, but limits for amp are -0.5V to 2.2V dc.

I would like to measure signal +-2V.

Thanks in advance to any help.

• Hi bohumilfulin,

The max input voltage range to the modulator is +/-3.2768V (vref = 4.096) with modulator common mode must be always 2.048V ( output of the diff amplifier). Meanwhile as mentioned the common mode input of the Differential amplifier can range from -0.5V to 2.2V. The input to the modulator can be +/-2.5V, the diff amplifier must  gain  the voltage to the required modulator input range.

There are two common mode here, one for modulator input ( diff amp output)which fixed at 2.048V and the other at the Diff amp input which is -0.5V to 2.2V.

Regards,

Jonathan

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Thank you,