my multisim simulation does not work in real world

[SampathBandara]

Hi

I am new one to the circuit world.

MY project is electric field measurement in thunderstorm. So I have plat plate antenna working as big capacitor and I need amplifier with high gain 500-1000) to amplify the signal I create the circuit but the problem is when I create in real world it does not work

Other problem is to reduce the DC offset I put the high pass filter for every end of the op amp output. So according to the theory its cut of frequency is about 212 MHz (calculation some time may be I am wrong) but I just need to reduce the DC offset my frequency range is (1 KHz to 50 MHz) how can possible to pass this frequency in my op amp circuit.

Please give me any suggestion 

[johnsold]

Is your problem with the simulation or with the circuit design? 

I do not have Multisim, so I cannot see your circuit. If you believe you have a circuit design problem, please post an image of the schematic diagram (.png). 

I just took a quick look at the OPA6951 datasheet. The input impedance may ba an issue if you are trying to measure the charge on a capacitor.

That frequency range has lots of strong signals from various radio services, so you may have other issues as well as just the circuit.

Lynn

[SampathBandara]

Thank for your reply .This is my circuit

[SampathBandara]

This is the idea of the antena

[johnsold]

Thank you. 

I have a few more questions.

1. Are C1 and C2 really 15 farad capacitors?

2. What is the estimated capacitance of the antenna?

3. What is the expected electric field and rate of change of the field at the antenna/capacitor? What kind of waveshape do you expect from real lightning and what are you using from XFG1 for simulation?

4. What are the input and output impedances of XBP1? It looks like you have two outputs connected together - XBP1 and U4.

5. You have pins 8 of the OPA6951 connected to VEE. What voltage is connected to VEE? The data sheet says Disable pin is usually left open for normal amplifier operation. It also says the typical enable voltage is 3.3 V.

Lynn

[SampathBandara]

Thank you

I am sorry I think I mad a mistake

here HFG1 is funtion generator

XSC1 is oscilloscope

out put connect to the DAC  Card

[SampathBandara]

I can understand what really happen here. By mistaken I put the 15F instead of 15pF but in real world I created the circuit using 15pF

I am sooooooooooooooooooooooooooooooooooo sorry

Any way now I have new problem

I have Large Dc offset in simulation can you give me  any suggestion to remove that  without losing the overall gain

[SampathBandara]

green colour one is my out put signal

[johnsold]

Without the capacitors you are amplifying the input offset voltages of the amplifiers.  The typical value is 0.3 mV and the maximum value is 3 mV at room temperature. The overall gain is enough to produce the output offset. So you probably need some capacitors between stages. The value should be chosen based on the lowest frequency signal component you need to amplify.

Lynn

[SampathBandara]

Thank you