peak detector : CS0951017

Hello rocco, 

I am not able to access the CSC link you provided.  Please provide a description of the question you would like answered. 

Thank you,  

~Leonard  

Number: CS0951017
Contact: rocco pochy
First name: rocco
Last name: pochy
Short description: peak detector
Phone: 15104380500
Email: rpochy@golighthouse.com
Company: Lighthouse Worldwide solutions
Company phone:
Language: English
State: Open
Provide case details or comments:

I am creating a peak detector circuit to capture pulses from 1-50us with a pulse height range from 5mV to 4V.  I have put simulated the issue with the circuit that outputs the peak height with a gain of 2X. Based on the design, I am not sure where this is coming from. I have included a TINA file that simulates the issue. I am looking for ideas or suggestions.

peak_detector.TSC

Hi Rocco,

you could do it this way:

rocco_ths4631.TSC

Or this way:

rocco_opa356.TSC

Kai

Can you explain why the initial design has the gain issue?

Hi Rocco,

not all OPAmps are equally well suited in a peak detector circuit. The OPA1678 is instable in this circuit, oscillates during the rising edge and is wildly overshooting. The following simulation shows the best performance that I could achieve with the OPA1678. But still instability can clearly be seen:

rocco_opa167x.TSC

The THS4631 and OPA356 are better suited here.

Kai

Since I am look at a low cost application. What op amp parameters do I need to address to avoid the oscillations in the circuit?  Ideally I am looking for a quad package. The suggested op amp are too expensive for the application.

Hi Rocco,

the OPA2301 could be used and the OPA2356.

Kai

What is it about the chips you choose that makes them good for this circuit?

Hello Rocco,

If you are interested in a quad package high speed op-amp, the most cost effective web price suggests the TLV3544.  You can compare the datasheet values for noise, output swing, power supply, and other requirements and see how it differs from Kai's recommendations.  I am not sure what your price target is; once you have an idea of your maximum cost you are willing to pay for a solution, you can investigate TI parts which are nearer to that value.

Kai's recommendations, all four of them, are well-suited to your application and are stable.  You will want to observe the stability of your circuit and be aware of oscillations and overshoot depending on the amplifier you select.  The higher the necessary performance with respect to noise, bandwidth, gain, output swing, and power consumption, the more expensive a product is likely to be.  Without knowing more system details, it is difficult for us to find you a recommendation.  

If you should need assistance in simulating various op-amps, I can help once I know more about your budget and performance concerns.   

Best,

Alec

Hi Rocco,

the TLV9064 is way too slow and it is instable:

rocco_tlv9062.TSC

The OPAmp should have a bandwidth of at least 200MHz in combination with a sufficiently high slew rate. The OPA356, OPA2356 and THS4631 fullfill this condition. But the TLV9062 has a bandwidth of only 10MHz.

The TLV3544 recommended by Alec can also be used with a slight quality loss for low input voltage steps:

rocco_tlv354.TSC

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rocco pochy said:

I would in interested in trying the TLV3544. How do I import the SPICE model into TINA?

Best you open the

TLV354x TINA-TI Reference Design (Rev. A)

and copy and paste the OPAmp into the orginal simulation.

Kai