UA741: uA741

Hi Neguse,

Yes, if you double click on the VG1 source, a menu will open. From there, you can click on the "three-dot menu" to the right of the "Signal" line. That will open your menu of input signal options which includes square waves, pulses, and more.

Thanks,
Paul

2604.AGC LM13700 Figure 20 & 42(3) (7).TSCHi Paul,

The circuit is supposed to takes an input of +22mV to +2V Pulse DC signal and amplifies with automatically control gain to get +3V DC output (regardless the change in the input). I run the circuit in simulation and tested with built circuit and the respond to changing input vs. output is not right. Do you have any suggestion?

Thanks,

Neguse

Hi Neguse,

I'll have to let Ron get back to you on this one - he's out right now but should be back before the end of the week. I thought your question was about using TINA!

Any additional information you're able to provide as far as bench data, waveforms, etc would be very helpful for Ron as he'll want to better understand in what way the circuit isn't working.

Thanks,
Paul

Hi Paul,

Attached are test result of the actual circuit and simulation.

Thanks,

Neguse

Neguse,

I saw that CH1 was the input pulse in the oscilloscope captures. I don't know if this is a single pulse or a repeating pulse. If repeating what is the repetition rate (frequency)? If there is just one pulse then the AGC will not have time to get to a final value (to equalize the AGC loop).

I saw CH2 is the output which normally runs at a high gain such that DC errors (input zero and LM13700 input offset voltages) make 3V output. Are the potentiometers set correctly? The calibration procedure is to apply 0V input (short) and adjust "P2" until U5 pin 5 is zero then adjust "P1" until U1 pin 5 is zero. Repeat this until both pin5 voltages are zero or as close as possible to zero.

For the simulation, setup VG1 to piecewise linear or import WAV to be your source input. Use AC analysis --> transient to see result. The oscilloscope feature is for repeating waveforms and is less accurate (in my opinion).

Ronald,

Changed to input signal:

I forgot to mention that now my input source is Pulse DC signal. The circuit is supposed to takes an input of +160mV to +3.8V Pulse DC signal and amplifies with automatically control gain to get +4V Pulse DC output (regardless the change in the input).

"The calibration procedure is to apply 0V input (short) and adjust "P2" until U5 pin 5 is zero then adjust "P1" until U1 pin 5 is zero. Repeat this until both pin5 voltages are zero or as close as possible to zero."

I am not sure if the above calibration procedure is correct, It seems that I can’t adjust P1 and P2 where pin 5 of U1 and U5 voltage are zero or as close as zero. Example, when I adjust P2 for U5 and set the voltage as close to zero and I measure the voltage at U1 the voltage goes up very high and vise versa. Is the issue with the circuit?

The attached transient result is VG1 set to piecewise liner input and the output is above 3V.

Regards,

Neguse G.

Neguse,

The calibration might have an issue if the AGC voltage changes during the calibration. To keep AGC at maximum, I suggest short U4 pin 2 to ground to get maximum U4 output (AGC signal). Are you using a 270 degree pot or a multi-turn pot. There is a lot of gain, so a 270 degree pot will be very sensitive (touchy).

Ronald,

I am using a 1 kOhms 1/4W Potentiometer 12 Turn.

Regards,
Neguse G.

Neguse,

That is a good choice for the potentiometer. Did the new calibration procedure work?

It is late in the process, but we haven't discussed the reason for this circuit (in detail). I understand that the input amplitude varies and the output amplitude should not vary. So I can assume that there is no intelligence (data) in the amplitude of the input signal. What characteristic of the input signal is of importance?