Multisim simulation problem

小朋友给我冲

Multisim simulation problem [Copy link]

Help! ! I designed three circuits, one is the first-stage amplifier circuit, one is the low-pass filter circuit, and the other is the second-stage amplifier circuit. The purpose is to amplify the 1MHz signal and filter the signal below 1MHz. These three circuits work separately and there is no problem with connecting the signals separately. After connecting the three circuits together, multisim started to report an error, and then the system automatically repaired it. After changing the frequency test, it works well below 1.7MHz, but it starts to report an error when the frequency exceeds this. Please help me, thank you! The following are the first-stage amplifier circuit, the low-pass filter circuit, the second-stage amplifier circuit and the circuit combined.

YC130

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小朋友给我冲

Sorry, the pictures are in reverse order

maychang

Why are three op amps used in the input stage?

Since the input signal is a single-ended signal, this stage can be connected as a common-mode amplifier using an op amp.

maychang

In addition, the gain of the first stage is so low, and the gain of the last stage is so high, can't the two stages be divided equally?

For low-pass filtering, it seems that the resistance is too small. Can we increase the resistance and reduce the capacitance? For example, increase the resistance to twice and reduce the capacitance to half.

小朋友给我冲

maychang posted on 2020-7-30 18:35 Why do we need three op amps in the input stage? Since the input signal is a single-ended signal, this stage can be connected to a common-mode amplifier with one op amp.

The first stage input is a double ended signal, I just simulated it this way.

小朋友给我冲

maychang posted on 2020-7-30 18:39 In addition, the first stage gain is so low, and the last stage gain is so high, can't the two stages be divided equally? For low-pass filtering, it seems that the resistor is too small. Is it possible...

Ok, I'll try to improve it. Thanks~

小朋友给我冲

My friend, please give me a push. Posted on 2020-7-31 09:03 OK, I will try to improve it. Thank you~

Hello, I modified it according to your method, and the combination of input stage and filter circuit, input stage and last stage, filter circuit and last stage, there is no problem in simulation, but when combined together to high frequency signal, it still reports an error. I would like to ask you for advice. Thank you~