Generating common mode voltage for AD779x

Hi,

  I'll get back to you soon. I am looking in to this.

Thanks,

Jellenie

Hi,

Regarding the selection of single to differential amplifier, I think someone from the ADC Drivers community might be able to help you. However, can you provide us more details regarding your target application? May I know also what is your input range and what supply voltage you want to operate? If you could also send us the schematic diagram, it would be great. 

Thanks,

Jellenie

Hi Jellenie,

thanks for the reply!

> can you provide us more details regarding  your target application?

I need to readout a photodiode for ultra low light intensities

> May I know also what is your input range and

the output of the ada4530-1 is only a few 10 mV

> what supply voltage you want to operate?

Supply voltage is 3.3V

Again, the general question is how to provide the required common mode

voltage (mid-supply) for the internal instrumentation of the AD7793

without the use of an additional single-ended->differential opamp.

Could well be that there is no way around to using that extra amplifier ....

Thanks

Peter

Am 20.09.2017 um 10:39 schrieb JellenieR:

  EngineerZone <https://ez.analog.com/?et=watches.email.thread>

    Re: Generating common mode voltage for AD779x

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Hi,

There's a restriction on the analog input range and common mode voltage when the in-amp is active. This will really requires you an analog front end to ensure that the limits are not exceeded for correct operation and to avoid linearity performance. So if your input is around 10mV, the negative input should be bias to at least 1V to meet the common mode requirements.

Would you like to consider using the AD7124, it has all the building blocks of the AD7793 with some advanced features. In AD7124, the common mode range must be between (AVSS − 0.05 + 0.5/gain) and (AVDD − 0.1 − 0.5/gain). The part can also accept a pseudo differential input so it can operate in a single ended application as it has a flexible MUX in which any analog of the analog input pins can be positive or negative input. So, in your application you can connect your single ended input to the one of the positive input and you can use the bias voltage midway between the analog power supply rails generated internally as your negative input. This generated bias voltage can be made available at any VBIAS pins and you can connect this to your selected negative input.

Thanks,

Jellenie

Hi Jellenie,

thank you very much for taking the time to answer my question.

I appreciate!

The AD7124 looks like a good part to solve my goal to omit the

extra opamp. I will look into your suggested solution.

Best regards

Peter

Am 25.09.2017 um 04:46 schrieb JellenieR:

  EngineerZone <https://ez.analog.com/?et=watches.email.thread>

    Re: Generating common mode voltage for AD779x

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