THS4531: offset understanding

Chris Willis

Intellectual 290 points

Part Number: THS4531

VOCM provides an output of supply/2 if left unconnected, zero if grounded, and voltage input level if voltage connected

the offset if applied after the gain

is that correct?

11 months ago

0 Anant Sinha 11 months ago

TI__Intellectual 1690 points

Hi Chris,

Below is the input circuit of Vocm pin.

If left unconnected (floating), the internal resistor divitor will set the output common mode voltage to mid supply.

This can be overdriven by an external source given it has sufficient current drive strength. In this case the output common mode voltage will follow the voltage at VOCM pin.

Regards

Anant

0 Chris Willis 11 months ago in reply to Anant Sinha

Intellectual 290 points

What if it is grounded, then zero offset?

Also, which is applied first, gain or offset? For example if my offset is 2.5V and gain is 2 and I feed in a signal of 1.5V, is it 1.5*2+2.5=5.5V or (1.5+2.5)*2=8V

0 Clemens Ladisch 11 months ago in reply to Chris Willis

Guru 287370 points

If V_OCM is connected to ground, then the common-mode voltage is ground. (This device does not have a GND pin and does neither know nor care where your ground is.)

A differential input of zero results in both outputs at V_OCM. So the gain must be applied first.

0 Chris Willis 10 months ago in reply to Clemens Ladisch

Intellectual 290 points

you stated "so the gain must be applied first"

to confirm, if my offset is 2.5V and gain is 2 and I feed in a signal of 1.5V, the output is 5.5V: it 1.5*2+2.5=5.5V. (output=input*gain+offset) Is that correct?

0 Nick Nauman 10 months ago in reply to Chris Willis

TI__Expert 6050 points

Hi Chris,

You are correct that the output would be equal to the input * gain then the Vocm voltage is added but not gained.

Thanks,

Nick

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THS4531: offset understanding