Amplifier in the oximeter

Wesley Huang

Other Parts Discussed in Thread: TLV9064

Hi team,

I have several questions about the application of the analog operational amplifier in the oximeter. Would you please answer them?

1. I see that TLV9064, a four channel operational amplifier of TI, is available on the market, and most of the schemes of oximeter on the market are four channel operational amplifiers. Do you know why the four channel operational amplifiers should be used in the application of oximeter? Why not 2 or 1 channel?

2. In the application of oximeter, what are the key parameters of op amp ? What are the benefits of improving these key parameters for the oximeter system?

3. Is there a reference circuit applied to the signal amplification of the front end of the oximeter? How much is the gain of this kind of amplifying circuit usually set? Why?

Best Regards

Welsey Huang

over 6 years ago

0 Ron Michallick over 6 years ago

TI__Guru**** 174826 points

Hello Wesley,

1) Four channels is the most cost efficient ($/channel)

2) It is all about the sensor , follow the sensor's guidelines for the amplifier stage.

3) Follow the guidance from the sensor manufacturer's data sheet.

I know this this is not especially helpful. I know a lot about TLV9064, but not the oximeter sensor.

0 kai klaas69 over 6 years ago

Guru 140200 points

Hi Wesley,

there's a TI oximeter reference design. You might want to have a look at it:

Kai

0 Ron Michallick over 6 years ago in reply to kai klaas69

TI__Guru**** 174826 points

Here is a second reference design.

https://www.ti.com/tool/TIDA-00311

0 Wesley Huang over 6 years ago in reply to Ron Michallick

Expert 1030 points

Hi Ron,

Thanks for your reply. I appreciate that. But i still wondering the key spec of the amplifier in the analog front of oxmeter and Notes on the design of the amplifier of the analog front end of the oximeter. Could you please answer my question generally?

Best regards

Wesley Huang

0 kai klaas69 over 6 years ago in reply to Wesley Huang

Guru 140200 points

Hi Wesley,

the key specifications are:

- Low supply voltage and low supply current for a battery powered operation.

- Input and output Rail-to-Rail for battery powered operation.

- Low input bias current and low input offset voltage for precisely working TIA (transimpedance amplifier).

- Low input noise for precise signal processing.

- Quad OPAmp availability for low PCB area.

Kai

0 Wesley Huang over 6 years ago in reply to kai klaas69

Expert 1030 points

Hi Kai,

Thanks for your reply.

How about the offset voltage ,offset drift and bandwidth? Does these specs has great influence in this kind of application in the oximeter?

Best regards

Wesley Huang

0 kai klaas69 over 6 years ago in reply to Wesley Huang

Guru 140200 points

Hi Wesley,

as Ron already mentioned, it mainly depends on the used detector diodes and LED sources. If you need a high gain somewhere in the signal chain, then the input offset voltage, offset voltage drift and bandwidth might be important key specifications.

Having said this, the signal frequency range of a typical oximeter is rather low. Low pass filters with corner frequencies of arround some hundreds of Hertz can often be seen in the signal chain of such circuits.

Kai

0 Ron Michallick over 6 years ago in reply to Wesley Huang

TI__Guru**** 174826 points

Wesley,

Generally the better the op amp the more accurate the system. Up to a point, where other factors will limit accary.

When in doubt, start with one of the reference designs and if desired make changes from that point.

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Amplifier in the oximeter