Design Inquiry

Hi AbhishekManoj ,

The ADC can accept +-4V based on the supplies you have sent. Please refer to the FAQ below on the analog input range of AD7768.

AD7768: What is the analog input range? - Documents - Precision ADCs - EngineerZone

The amplifiers ADA4940 and ADAD4945 can work using single ended to differential output to drive the ADC. Please refer to the link below for suggested ADC drivers using different ADCs.

Precision ADC Driver Tool | Analog Devices

Thanks,
Janine

Hi Janine.

From the table you had shared, sorry that I didn't get it completely. I'm providing unipolar supply for ADC AVDD-5V and AVSS-Ground. 

From the above table, for 5V AVDD and 0V AVSS, the range is only +4.096. I had asked for +/-4V range which includes from -4V to +4V, 8Vpp.

Does it support the above voltage range.

For the above requirements can i give +5V and -5V supply for the amplifier ADA4945-1.

Also, please address some more queries regarding AD7768.

1.ESD Protection diodes part number AINx inputs as mentioned in datasheet. Or is those mentioned ESD diodes are internal to the IC.

2.In AD7768 evaluation board AIN pin connected directly to ground?

3. In evaluation board separate amplifier is used for AIN+ and AIN-. I'm using a single amplifier to convert single ended input to differential pair to the ADC input. Do I need to provide the below mentioned circuit between AINx+ and AINx-

4.I'm using ADA4945-1 as input amplifier to ADC, IN- pin i will connect the incoming input signal. IN+ pin how should I terminate or does i want to VCM_OUT to this pin.

5.Where should I connect VCM pin of the ADC.

6.What does the VCOM pin features and use in evaluation board, the VCM_out and AVDD1 is connected to an opamp OP2177 and the output is VCOM which is fed to IN+ of the ADC input amplifier. Can you please explain this circuit working.

7.For AVSS i need to provide analog ground or normal ground.

8.For pull up and pull down for FILTER and MODE pins, which resistor value should I use to pull to AVDD and GND. Can I use 10K resistor for that purpose.

9.For REFx pin ground, should i give analog ground or digital ground.

10.I'm not using XTAL1 pin as I'm using CMOS Clock. How should I terminate XTAL1 pin.

11.Which values should be given to XTAL1 and XTAL2 optional termination resistor and capacitor

Regards,

Abhishek

Hi JEstayo 

For my unused DOUT signals DOUT6 and DOUT7, how to terminate, should i make it as NC. As these pins termination details is not mentioned in datasheet.

I'm attaching the schematics of AD7768 and schematics of AD7768-4 of my board.

Please review and provide your feedbacks.

1.AD7768 with 6 channels used

PDF

2.For AD7768-4 with input amplifier

PDF

Regards,

Abhishek

Hi Team,

Please provide an update on above.

Regards,

Abhishek

Hi AbhishekManoj ,

For unused DOUT pins, please connect these pins to ground through pull-down resistors.

I will review the remaining part of the schematic and get back.

Thanks,
Janine

Hi JEstayo 

In my board I'm planning to use RF cage for the separately for each ADC and DAC.

In my board there is a total of 3 ADC ICs. While selecting the cage, is there any recommendations for the spacing from ADC IC or height anything like that.

Also the RF cage must be provided for the ADCs including its surrounding components. Does the ADC input amplifiers also should be covered inside the RF cage.

Also please provide the schematic review feedbacks.

Regards,

Abhishek

We recommend driving the reference pin using a precise voltage reference, such as ADR4540 or ADR445 (refer to Figure 73 in the datasheet), unless VREF_4V originates from a precision source. Noise or drift on vref directly affects the gain error. Using high-quality voltage references ensures stability, low noise, and high PSRR, which are critical for optimal performance.

Do you observe any performance degradation during your RF frequency tests ? We recommend conducting initial testing without the RF cage to establish a baseline.

Hi PVP 

For 4V reference, i had used ADR444BRZ IC.

Please provide the review feedback on the above shared schematics.

We are in our design phase, checking the RF cage for the ADCs.

Regards,

Abhishek

Hi PVP 

For 4V reference, i had used ADR444BRZ IC.

Please provide the review feedback on the above shared schematics.

We are in our design phase, checking the RF cage for the ADCs.

Regards,

Abhishek

Hi team,

Please provide an update on above.

Regards,

Abhishek

Hi,

Regarding the RF cage, it is recommended to cover the Amplifier, ADC, and AAF together. If there are any tall components in the signal chain, the cage height will need to be considered accordingly. 

Hi,

Regarding the RF cage, it is recommended to cover the Amplifier, ADC, and AAF together. If there are any tall components in the signal chain, the cage height will need to be considered accordingly.