Wien bridge with 120MHz frequency

simon01920 · Oct 19, 2022

Hello guys,

I am writing here for the first time, but I am really desperate. I already wrote on the NI forum, but the root of the problem was still not solved. The assignment says that I should make a Wien bridge that oscillates with 120MHz frequency. However, no matter how I try with my current scheme I can't seem to get the desired frequency and I'm capped at 112MHz which seems to be the maximum. What changes should I implement, so I can complete the assignment successfully?
Also, I have made this in multisim 10.0.1, tried to open it in 14.2 but no luck.

This is the one I created.

This schematic was created by a user of the NI forum, but the same problem. (I include both files the one I made is .ms10 and the one created by a user of the NI forum is .ms14)

I'd need something around 120MHz (margin - 1MHz up/down) on the frequency counter to complete the assignment successfully.

Alec_t · Oct 19, 2022

Welcome to maker.pro!
You need a faster op-amp. From the datasheet, the unity gain bandwidth is only 120MHz.

simon01920 · Oct 19, 2022

Alec_t said:
Welcome to maker.pro!
You need a faster op-amp. From the datasheet, the unity gain bandwidth is only 120MHz.

But which one? I dont think the op-amp is the problem because with that different schematic and the same op-amp we could have GHz and 100ths of MHz.

bertus · Oct 19, 2022

Hello,

As @Alec_t said, you will need a faster opamp.
A wienbridge oscillator works at a gain of 3.
The opamp needs to be able to provide that gain.
I would recommend an opamp with a GBW of minimal 500 MHz.

I also would say that a wienbridge oscillator at 120 MHz using opamps is unrealistic.

120 MHz oscillators are usualy made with a LC circuit.
Harley and colpitts oscillators can be used: