Electrical – LTspice Sample Hold

The LT1028 is intended for operation from +/- 15 volts, and is only speced as low as +/- 5 volts, and you are running it at 3.3 single-ended. Try changing V2 to 30 volts.

There a few problems with your circuit:

1) The second stage will generate an exponential rather than a triangle. 2) The resistor values for feedback on the second stage are much too low - the amplitude may be limited by the output current capability of the 741. You can use something in the range 10k-100k. 3) The actual amplitude of the output will be limited by the opamp. The 741 os a very ancient opamp and is not as good as more modern ones - as Peter mentioned the output cannot get closer than ~2.5v to the rail.

This configuration should give better results:

It still uses two opamps and only needs one capacitor to set the timing.

The first stage is arranged as a schmitt trigger to detect when the output of the second stage reaches voltages determined by resistors R1 and R2. The second stage is configured as an integrator and will produce a triangular wave with linear slopes.

The square wave output is still determined by the saturation of the opamp as before, an opamp with rail to rail output will get very close to the supply rails.