# +-3 to differential ADC, without oamp?

1. ## +-3 to differential ADC, without oamp?

Hi,

I use a vibration sensor that generates a signal +-3V ( +-3V signal, AGnd). I want connect sensor to the differential ADC converter (V+ V- GND).
Is it possible to connect such a signal without any amplifier?

I have to questions:
1) Can I connect the signal in the following way: +-3V signal to V+ , AGnd to GND, V- "not connect" ?
or
2) Do I have to use a differential amplifier to match the signals? In books he writes about 0-3V signals, and I have + -3V. Schemes in the books say that the signal must be for range 0-3V. I have + -3V. signal

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2. ## Re: +-3 to differential ADC, without oamp?

You need to study the adc spec in detail. Not connect an input is rarely a solution.

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Signal -> V+
Agnd -> V-
Agnd -> GND

?

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4. ## Re: +-3 to differential ADC, without oamp?

You are not making much sense. Forget about what "the book says". What book? Look at the data sheet for the ADC. What does THAT say? You gave us absolutely no information about the ADC in question.

5. ## Re: +-3 to differential ADC, without oamp?

I use a measuring card designed by a no-name company. I got such measuring equipment at the university. I apologize for the lack of specifications. I only have this information:

"The differential input signal has a maximum positive value when input V+ is at +5 V and input V− is at −5 V. It has a maximum
negative value when V+ is at −5V and V− is at +5 V. The input impedance is 100 KΩ on each input with reference to 0 VA"

It seems to me that if it's just one sentence ... Is it enough information? However, I do not understand it completely. Can I connect my symmetrine signal +-3V to this card, or do I have to add a different amplifier?

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My analysis:

3V -> V+
gnd -> V-
"V+" - "V-" = 3V - 0 = 3V max signal

-3V -> V+
gnd -> V-
"V+" - "V-" = -3V - 0 = min signal

it looks like it will work. However, in this case, do I have to connect the AGND sensor to the GND input of ADC? I understand that "GND" ADC is Vcom? Am I wrong?

Sensor +- 3V signal to "V+" of ADC
Sensor AGND to "V-" of ADC
Sensor AGND to "GND" of ADC (???)

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Pins descripitions:
Pins description
1) "VA" - V analog return for analog circuitry.
2) "V+" External differential positive analog detector signal. ±11 V full scale. Input.
3) "V-" External differential negative analog detector signal. ±11 V full scale. Input.
4) "VA" analog return for analog circuitry.
5) "+12V" analog for any analog circuitry. Do not pull more than 100 mA from this pin.
6) "−12V" analog for any analog circuitry. Do not sink more than 100 mA into this pin
7) "nc" not connected
8) "nc" not connected
9) "nc" not connected

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