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# TLV07: Why are low values of resistor causing gain peaking?

Part Number: TLV07

I am trying to simulate frequency response of TLV07 in non-inverting configuration for gain 10 as shown below:

The frequency response shows peaking as shown below:

It is worse for smaller values of resistors like 1 and 10:

The response is considerably better for 1k and 10k:

What is the reason for this? In my understanding, peaking is generally seen at higher values of resistances because of influence of parasitic capacitors but here I am observing the opposite behaviour.

• Hi Darrell,

the TLV07 is a 600R OPAmp or by other words can drive 600R loads. But in your circuit it sees an effective load of 110R which means a short-circuit at the output. Don't expect the OPAmp to be longer working in linear operation with such a short-circuit.

Kai

• How is the effective load value calculated? I don't get why adding the feedback and R1 resistor is the effective load seen by opamp.

• Hi Darrell,

an OPAmp must not only drive the classical load but also the feedback resistors. Both are connected from the output to signal ground

The load is the total resistance from the output to signal ground which is 100R + 10R = 110R here.

Kai

• Hello Darrell,

More specifically, these RRout op amps have a complex and higher open loop output impedance that is interacting with that 110ohm feedback load to reduce the phase margin at LG=0dB crossover. This is a relatively new part so it will have a very thorough GWL TINA model including that Zol model, that will be trying match this plot I would suspect, there has been quite a lot of work to soften the resonances in these, but still kind of high if you think about this open loop Zout driving that load,

Anyway, running this in a LG sim with your set up gives 45deg phase margin at LG=0dB xover at 25.5kHz.

That, in theory, should be producing about 2.2dB peaking in the closed loop design via Figure 2 in this article, which also talks about setting this sim up,

https://www.planetanalog.com/stability-issues-for-high-speed-amplifiers-introductory-background-and-improved-analysis-insight-5/

It is always easy to test this effect by inserting a gain of 1 dependent source isolating the Zol from the load,

Here that is in the LG sim emulated the specified load of 10kohm into the VCVS at the output. Yes, 86deg phase margin and quite a lot wider BW,

Here is the LG file if you want to exercise different Rf values, That Figure 2 in the article is a 2nd order LG analysis, you are getting even more peaking since the loop is higher order.

TLV07 LG sims.TSC

• Thank you for such a detailed reply!

• Thank you Kai and Michael. I will go ahead and close this thread now.