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OPA836: How to implement a buffer using OPA836?

SK
Intellectual 260 points
Part Number: OPA836
Other Parts Discussed in Thread: OPA659

Hello,

How to do a buffer with OPA836?

I attached my simulation, please take a look.

OPA836.TSC

The op-amp operates in single supply of 5V.

The input signal is DC to 60MHz, and the amplitude is 1V.

R1 and R3 are performing as an attenuator, and the input impedance must be 1M ohm.

I followed the schematic of the figure 60 in OPA836 datasheet. My simulation is a noninverting single supply with reference voltage 1V.

But the output signal seems wrong.

  • 0
    Guru 48395 points

    Morning, 

    Your resistor values are too high for this device, 

    1. It specifies a 200kohm CM input R with 1.2pF

    2. Even without that input R, you need speed up caps to remove the parasitic pole to the V+ input

    3. Your feedback and gain Rs are way too high for stability, try about 1k and 1k, will lose bias current cancellation

    4. The output pin will not drive to 0V on single supply, consider using the LM7905 to get a -0.23V negative supply

  • 0 in reply to Michael Steffes
    TI__Expert 3486 points

    Hello , as the input impedance required is 1Mohm , i would recommend using a CMOS/FET input amplifier like the OPA659, 

    As i can see you are interested in the 60Mhz for an amplitude of 1Vp i would recommend to look at the large signal BW of the opamp rather than the small signal BW . This is typically given in the graph section of the datasheet , OPA659 will suit your needs :) 

    It will be very easier for you if you can generate a negative source as your incoming signal is both positive and negative .

  • 0
    Guru 140200 points

    Hi,

    why have you chosen the OPA836? Because of the low supply current?

    Why have you chosen figure 60 as reference? Your input signal is not swinging arround a bias voltage of 2.5V.

    Why must the input impedance be 1M? In this case you should look for an OPAmp with low input bias current.

    Can you tell more about your application?

    Kai

  • 0 in reply to kai klaas69
    Guru 140200 points

    How do you proceed?

    Kai