Multi-channel ADC

Yu Geng

Other Parts Discussed in Thread: TIDA-00294

Hi, I'm looking for the multi-channel ADC which can measure the analog signal (+-2V), with wide bandwidth(1M)

I have one option is ADC342x Quad-Channel, 12-Bit, 25-MSPS to 125-MSPS, Analog-to-Digital Converter.

But I have doubt in the datasheet.

It has a specific pin for the common mode input(Pin 27). Is it for the input analog signal or the output? What is the purpose of this pin? And do I need to worry about the input common mode level? I have four signal with different CM level.

over 8 years ago

0 Joseph Wu over 8 years ago

TI__Guru* 94045 points

Yu,

Since this question is about the ADC342x series of data converters, I'm moving this post to the High Speed Data Converter Forum. The engineers that look over that part will be able to find this post here.

Joseph Wu

0 Yu Geng over 8 years ago in reply to Joseph Wu

Prodigy 130 points

Thank you !

0 Jim Brinkhurst1 over 8 years ago in reply to Yu Geng

TI__Mastermind 44550 points

Hello Yu

The ADC342x devices must be driven with a differential signal which is centered around the VCM common mode voltage of the ADC.

If you don't need to capture the DC level of your input signals, you can use a transformer coupled drive circuit similar to that shown in Figure 183 of the datasheet.

If you also need to capture the DC information, you will need to use a differential amplifier to perform single ended to differential conversion, and common mode shifting.

The information in TIDA-00294 (http://www.ti.com/tool/tida-00294) addresses both types of configurations and may be helpful.

There are additional TI Designs that may also be useful here:

http://www.ti.com/lsds/ti/amplifiers-linear/fully-differential-amplifier-overview.page

Best regards,

Jim B

0 Yu Geng over 8 years ago in reply to Jim Brinkhurst1

Prodigy 130 points

Hi，

I want to use this 4 channels ADC to measure 4 different analog input.

the common mode is different for all this four input. how can I set the four different input common mode in this IC?

0 Jim Brinkhurst1 over 8 years ago in reply to Yu Geng

TI__Mastermind 44550 points

Hello

The input signals to the ADC must be differential with the proper amplitude and common mode voltages as specified in the datasheet.

If your input signals are single ended you must design an amplifier circuit that can translate each signal to differential with the necessary common mode voltage and provide gain or attenuation as needed.

If your input signals are already differential, your amplifier circuit just needs to shift the common mode voltage as needed, along with the needed gain or attenuation.

The references provided in my previous response should help you design the necessary amplifier circuits.

Best regards,

Jim B

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Multi-channel ADC