PGA 308 bipolar signal input

1282634

Other Parts Discussed in Thread: PGA308, THS4521, PGA309

Hi,

Just wondering can I apply bipolar signal input to PGA 308?

Do I need to pseudo-bias the signal to the mid range of the supply voltage? Is there any reference design I can refer to regarding my problem?

Thank you.

over 12 years ago

0 Ian Williams over 12 years ago

TI__Mastermind 27715 points

Hello,

What kind of signal are you thinking of using as the input to the PGA308? The front-end of the part is an instrumentation amplifier, so it's expecting a differential input signal relative to a common-mode DC bias (typically mid-supply).

Best regards,

Ian Williams
Linear Applications Engineer
Precision Analog

0 1282634 over 12 years ago in reply to Ian Williams

Prodigy 200 points

Hi Ian,

I am grateful of your swift reply.

The output of my sensor has the following characteristics:

1. It is single ended

2. Bipolar sinusoidal signal centered at zero.

3. In the range of 5mV to 50mV peak to peak.

May please favourably advised on how I should precondition my signal in order to use PGA 308?

Thank you.

0 Ian Williams over 12 years ago in reply to 1282634

TI__Mastermind 27715 points

Hello,

Can you please specify your input signal bandwidth? Also, what is the output impedance of your sensor?

Best regards,

Ian Williams

0 1282634 over 12 years ago in reply to Ian Williams

Prodigy 200 points

Hi Ian,

The bandwidth is around 100kHz and the output impedance is around a few hundred ohm.

0 1282634 over 12 years ago in reply to 1282634

Prodigy 200 points

Thanks.

0 Ian Williams over 12 years ago in reply to 1282634

TI__Mastermind 27715 points

Hello,

One solution is to use the THS4521 - a fully-differential amplifier with sufficient bandwidth and an input common-mode range of 200mV below the negative supply. This is convenient for your application since the PGA309 is a single-supply amplifier, and you could use the same supply for the THS4521 while still remaining within the input voltage specifications.

I've attached a circuit in TINA which does this. I'd recommend staying in a gain of 1 in order to allow the PGA308 to properly scale the gain and offset of the sensor to the typical 0.5V to 4.5V output.

Best regards,

Ian Williams

EDIT: The original post did not contain the attachment, but it is now uploaded.

Single-ended to Diff.TSC

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PGA 308 bipolar signal input