TINA/Spice/LMH6702: Small Signal Frequency Response

Hiroshi Katsunaga

Mastermind 6480 points

Part Number: LMH6702
Other Parts Discussed in Thread: TINA-TI,

Tool/software: TINA-TI or Spice Models

Hello,

I have a question about LMH6702 Spice Model.

[Q]

The specifications of LMH6702 are as follows.

* SSBW(SM)=1700MHz

* SSBW(LG)=720MHz

* Transimpedance is showed with Figure 19

The Simulation Results are as follows.

I simulated with non-inverting configuration with RF=237ohm, RG=237ohm, RL=100ohm, V+=5V, V-=5V.

* -3dB BW=575MHz @AVCL=+2

* Transimpedance is close to Figure 19 of the D/S.

* Dominant pole = 318kHz

Is this device really small signal bandwidth 1700MHz ?

Is this just a modelling issue ?

Best Regards,

Hiroshi Katsunaga

over 5 years ago

0 kai klaas69 over 5 years ago

Guru 140200 points

Hi Hiroshi,

hmm, figure 3 of datasheet looks like a typical package resonance. Such a package resonance can extend the bandwidth of an OPAmp because of parasitic capacitances. If you run a TINA-TI simulation you can easily check this out by adding some parasitics:

Without parasitics the bandwidth is about 700MHz and with parasitics the bandwidth is 1GHz.

Kai

0 kai klaas69 over 5 years ago in reply to kai klaas69

Guru 140200 points

Sorry, forgot the TINA-TI file:

hiroshi.TSC

Kai

0 Hiroshi Katsunaga over 5 years ago in reply to kai klaas69

Mastermind 6480 points

Hi Kai,

Thank you for your fast response.
I think that the parasitics are not modeled as you say.
However, it seems that it is not all.
snom144 (PSpice Model) have text document. This model is same as TINA-TI macro model.
It describes the model performance.
My understanding is as follows.
* This model seems to be modeled @ Vout=2Vpp w/o parasitics even by small signal AC analysis.
* Therefore this model is not able to simulate true small signal analysis at Vout=0.5Vpp.
What do you think ?

Best Regards,
Hiroshi Katsunaga

0 kai klaas69 over 5 years ago in reply to Hiroshi Katsunaga

Guru 140200 points

Hi Hiroshi,

in TINA-TI you will find a difference for small signals and large signals. Make a transient analysis and check the sine frequencies 500MHz and 700MHz. The frequency response differs quite a lot for 0.25Vpp and 1Vpp input signal.

Kai

0 Hiroshi Katsunaga over 5 years ago in reply to kai klaas69

Mastermind 6480 points

Hi Kai,

OKay, I understood the limitation of the model.

Thank you for your cooperation.

Best Regards,
Hiroshi Katsunaga

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TINA/Spice/LMH6702: Small Signal Frequency Response