# AD7768 : 8 CHANNEL ADC CAN SUPPORT SINGLE END - BIPOLAR INPUT.

Hi All ,

I have an requirement to convert the 8 channel analog input (Single ended - bipolar) signal with the range of 10Vpp, The waveform will be sin, ramp, square,and Sweep.

Hence I am planing to use AD7768. In this I need a clarification of following points:

1. I have 8 channel single ended bipolar signal inputs (10Vpp, +/- 5 ), So I will connect this signal to the correspoding port of (AIN0+ to AIN7). My question is, May I Ground it the remaining ports of AIN-0 to Ain7- ?

2. My input signal should support (+5V to -5V , 10Vpp), so in REF1- and REF2- may I connect to Ground or -2.5V should give ?

3. If I ground the REF1- and REF2- , The AD7786 support the input signal swing 10Vpp?

4. Even though My Signal is single ended bipolar , Is there I want to make this signal to converted into differential bipolar (True Biploar signal)?

Please clarify the points as soon we are going to finalise the design stage.

Parents
• Hi Sidiq,

You can use a fully differential amplifier like the LTC6363 or ADA4940 to perform this function. This will allow you to use the full range of the AD7768. Please note you will need to use a 5V reference such as ADR4550. The picture included below is from the LTC6363 datasheet which you will find here. In this type of configuration both AIN+ and AIN- are connected to the LTC6363 outputs. REF1- and REF2- can be connected to ground since the common mode output from the AD7768 can be used to set the common mode of the LTC6363 to 2.5V.

Regards

Niall

• Hi Sidiq,

You can use a fully differential amplifier like the LTC6363 or ADA4940 to perform this function. This will allow you to use the full range of the AD7768. Please note you will need to use a 5V reference such as ADR4550. The picture included below is from the LTC6363 datasheet which you will find here. In this type of configuration both AIN+ and AIN- are connected to the LTC6363 outputs. REF1- and REF2- can be connected to ground since the common mode output from the AD7768 can be used to set the common mode of the LTC6363 to 2.5V.

Regards

Niall

Children
• Hi ,

Hope you are well.

I was going through this forum and I saw the explanation of LTC6363. In the previous explanation, we can use LTC6363 as

1. Filter

2. Single/Differential to Differential Converter

3. Attunator

But my query is that If we can use this amplifier for all above operations then what is the need for keeping LPF in the analog chain as Mr. Mohhamad added in analog signaling for ADC7768?

• Hi Kapiliitd,

Depending on the level of anti-aliasing filtering required it may sometimes be necessary to have a higher order filter in order to have a sharper roll off. In this case, a 3rd or 4th order filter should be sufficient. Page 57 of the AD7768-1 datasheet explains the anti-aliasing requirements for this family of sigma delta ADCs. (AD7768/AD7768-4/AD7768-1)

Regards

Niall