Understanding how the sampling integrator works

[waltr]

Attached is a text file of Carl's explanation (copied from a forum post) of how a sampling integrator works. Was very helpful to me.
IntregratorDesign.txt

[green]

Hello all,
I am trying to learn from how the Baracuda works.
I have difficulties in understanding how the sampling integrator is operating. I do not currently have a Baracuda itself and it seems to be out of stock in the diyDetector store. I'll place a separate post in the trade section of the forum to try and obtain one.
Until I get one, I am trying to theoretically analyze (LTSpice simulation) and understand the operation of the integrator itself. I was already able to separately build the preamp and TX circuit, so I am able to get a meaningful signal out of the preamp circuit. I measured this signal with a scope, I captured the waveform in digital format and I am able to feed it (in the LTSPice simulation) to the input of the integrator. The picture below indicates the LTSpice simulation circuit. The V7 supply is a PWL source generating the output of the RX preamplifier, as I have captured it with the oscilloscope. I have simulated the Q2 and Q3 transistors with ideal switches.

LTSpice simulation circuit

The picture below shows a period of the RX amplifier output, and the timing relation of the Main and Secondary pulses.

Single period RX Preamplifier signal

I run the simulation by repeating this single period at the input of the integrator a number of times (1kHz repetition rate). The voltage at the output of the integrator gradually increases during each period, until it gets into saturation (see next image below).

Multiple period RX Preamplifier signal and integrator output

From the documentation, however, I understand I should obtain a DC signal at the output of the sampling integrator. Any idea on what I am doing wrong?

Best regards,
Cristian

Your target simulation looks like what I would expect for no target. Looks like you start sampling when the amplifier is still saturated, to soon.

[brumbarchris]

Hello all,
I am trying to learn from how the Baracuda works.
I have difficulties in understanding how the sampling integrator is operating. I do not currently have a Baracuda itself and it seems to be out of stock in the diyDetector store. I'll place a separate post in the trade section of the forum to try and obtain one.
Until I get one, I am trying to theoretically analyze (LTSpice simulation) and understand the operation of the integrator itself. I was already able to separately build the preamp and TX circuit, so I am able to get a meaningful signal out of the preamp circuit. I measured this signal with a scope, I captured the waveform in digital format and I am able to feed it (in the LTSPice simulation) to the input of the integrator. The picture below indicates the LTSpice simulation circuit. The V7 supply is a PWL source generating the output of the RX preamplifier, as I have captured it with the oscilloscope. I have simulated the Q2 and Q3 transistors with ideal switches.

LTSpice simulation circuit

The picture below shows a period of the RX amplifier output, and the timing relation of the Main and Secondary pulses.

Single period RX Preamplifier signal

I run the simulation by repeating this single period at the input of the integrator a number of times (1kHz repetition rate). The voltage at the output of the integrator gradually increases during each period, until it gets into saturation (see next image below).

Multiple period RX Preamplifier signal and integrator output

From the documentation, however, I understand I should obtain a DC signal at the output of the sampling integrator. Any idea on what I am doing wrong?

Best regards,
Cristian