OP07: How to suppress noise under given threshold？

Hi Guohong,

Guohong Zeng said:

to amplifiy part of the input signal when it is larger than given threshold, otherwise output zero.

There are no single integrated IC that are designed for this application. You have to put 2 or 3 discrete circuit together for the application. 

I need to know the following:

1. specific frequency or range of frequency.

2. input signal comparator threshold

3. gain factor and op amp's supply rails. 

For a part of combo in op amp + comparator in package, we have TLV2704/TLV2704 that may handle the threshold comparisons and input signal amplification. TLV2302/TLV2304 may not able to handle the functionality. The product is likely supported by LVAC team. 

If you use separate comparator, you may need to use op amp with Enable/SHDN feature to implement this, such as TLV9062S, TLV9052S

Please let us know what type of application is this. You need to need to use BPF to filter out unwanted frequency and amplify the specific input frequency for the application. Please provide us the application details. 

Best,

Raymond

Hi, Raymond,

Thank you for your constructive reply.

I want process the signal from ultrosonic transducer, and find there is some background noise, although no more than 1/10 of the echo pulse train.

As the noise can make the Receiver signal strength indication (RSSI) circuit output some  fluctuation, which is tricky in designing the algorithm to find the normal echo.

This is the reason that I want to suppress the noise by hardware, before it enter BPF and RSSI circuit.

The signal frequency is about 100kHz,  amplifier total gain is about 30, supply rail is -3.3V~+3.3V.

I want to change compare threshold using D/A, and set it through automatic online calibration in the application stage.

Best Regards,

Guohong

Hi Guohong, 

Guohong Zeng said:

The signal frequency is about 100kHz,  amplifier total gain is about 30, supply rail is -3.3V~+3.3V.

Here is an example in driving ultrasonic transducer. With gain of 30V/V, you need have op amp with GBW > 6MHz (ultrasonic frequency is 100kHz)

https://www.ti.com/lit/ab/sboa502/sboa502.pdf?ts=1755487671373&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct-category%252Famplifiers%252Fop-amps%252Fpower%252Foverview.html

Guohong Zeng said:

This is the reason that I want to suppress the noise by hardware, before it enter BPF and RSSI circuit.

First of all, you should capacitive couple the ultrasonic transducer. 

2nd, you need to have BPF that is operating and centered at 100kHz, HPF and LPF are configured around 100kHz, depending on your requirements (narrow or wider BPF). 

You have RSSI circuit - it sounds like that this may be distance or flow meter application. To have receiver 100kHz signal, you may need to have narrow BPF to eliminate environmental interference. You may need 2nd to 4th order BPF filter to attenuate unwanted frequency. 

It is still unclear that you are looking for ultrasonic driver (driving current or load) or ultrasonic receiver or both. Please provide a schematic or block diagram what the requirements are. I may be able to provide some suggestions, if I understand the application fully. 

Best,

Raymond