Tool/software:
HI,
I planned to use JFE2140 as 20dB gain amplifier to drive a transducer up to 80 kHz. Below is my simulation model in LTspice.
I use the JFE2140 Pspice model
What I notice from my model and the measurement is behave differently. Most of the resistor in simulation is 0.1% thin film resistor. I got around 20dB gain in my measurement, but it seems it is fluctuating.
Could you please check?
01 Preamp.zip
Hi Andri,
We cannot support LT spice simulations. For this reason I have recreated the circuit inside of Tina Ti which is a free download here:
https://www.ti.com/tool/TINA-TI
My simulation can be found at the bottom of this post.
Looking at the DC bias it looks like the IDS current is fairly low. I also see a gain of 11.92dB or approximately 4V/V.
The gain is a function of the transconductance gm parameter.
Adb = 20*log(gm*Rd).
Therefore with the simulated gain we can back calculate gm.
or approximately 3.5mS which is roughly in agreement with the plot below.
To verify this theoretical calculation we can simulate gm as shown below and calculate the linear gm value. My gm simulation is also found at the bottom of this post.
Calculating the linear gm value I get roughly 3.6mS which is in alignment with the prior two analysis approaches.
Can you check you DC bias points with this information to see if we are in alignment?
JFE2140 gm simulation.TSC6835.JFE2140.TSC
Best Regards,
Chris Featherstone
Hi Chris,
Thank you for prompt response.
is it fair to say if I increase Ids than I will get better gain?
below is my update of the simulation. in your opinion, what is the best way to increase the gain for this circuit while maintain its stability?
I am still new to TINA TI, I am unable to reproduce the gm graph on your second sim file.
The updated sim 0602.JFE2140.TSC
Hi Andri ,
Yes increasing the IDS current will increase the gain. I have simulated and added the instructions on how to run the gm simulation below. With the new IDS current the gm is now approximately 10.28mS.
Note that your Vds voltage is in a good operational point of 1.74V. If Vds is modified too high you will increase your gate current. I just point this out so you are mindful of Vds if you adjust the values in the future.
The gm parameter can vary by 30% over process. If you need a closed loop predictable gain solution over process and cannot tolerate a 30% variation over process, I have written an application note for one such possibility below.
For a fully differential closed loop solution I am running another thread here that has those possibilities as well.
I hope this information is useful.
Best Regards,
Chris Featherstone
