Below is the LTspice simulation of Alec's basic circuit with an opamp to perform the switch function to invert the polarity of the input op amp.

Due to finite response times of the op amps, there is a glitch during the sawtooth flyback.
This is reduced by the R6-C2 filter.

View attachment 149160

Thank you everyone for your great help! The circuit is simulating great without any issues. I have included the 9V supply and MC330 op amps that will be used. I was hoping to get the triangle wave so that it would oscillate with an average voltage of zero (-2.5 V offset). Any ideas how to achieve this ?

 

First, you will need bipolar power supplies for at least the output opamp. For a fixed offset, replace R7 with two resistors that create a Thevenin equivalent DC offset. For an offset that tracks the actual amplitude of the waveform, AC couple the input to U3A.

ak

 

So I have connected the actual sawtooth source, which is displayed in red on the Oscilloscope below. A triangle wave is produced however again there seems to be an issue with it. Connecting a saw tooth generator of the same frequency and offset as the source gives a perfect triangle output. However it doesn't seem to work using the source. Changing the value of Rs6 to 1kHz cleans it up a bit, but it also seems to decrease the amplitude. Is it possible to get a cleaner signal?

Rs6 at 10kHz:

Rs6 at 1khz:

 

It looks like Q1 is resetting C1 before the end of the cycle. Also, the red trace is not symmetrical about GND.

ak

 

The problem is that the precision rectifier has a different input impedance for the top half of the waveform as compared to the bottom half, which causes a DC offset of the waveform through the capacitor and thus distortion of the rectified output.

One solution is to add a follower op amp between C3's output and the precision rectifier input.

 

I added a follower, but the problem persists. What values need changing to alter the symmetry of the sawtooth? I really am stumped with this, I was hoping to start building tomorrow!

 

What problem?
All I see in the normal glitch near the peak of the waveform.

 

Below is the LTspice simulation of Alec's basic circuit with an opamp to perform the switch function to invert the polarity of the input op amp.

Due to finite response times of the op amps, there is a glitch during the sawtooth flyback.
This is reduced by the R6-C2 filter.

View attachment 149160

I wonder if you could explain this circuit in a bit of detail, I understand that the rectifier blocks any negative part of the waveform. But what are the other 2 op amps configurations ?

 

I wonder if you could explain this circuit in a bit of detail

When the input is negative, U5 turns on and keeps node 2 at ground through D1.
This means U4 acts as an inverter with a gain of -1 to convert the negative input voltage to a positive voltage.

When the input goes positive, U5's output goes to 0V.
This allows node 2 to see the positive input voltage.
U4 then acts as a follower with a gain of +1 (applying the same voltage to the inputs of the opamp makes it act as a follower).
U6 is just a buffer for the RC glitch filter.

 

When the input is negative, U5 turns on and keeps node 2 at ground through D1.
This means U4 acts as an inverter with a gain of -1 to convert the negative input voltage to a positive voltage.

When the input goes positive, U5's output goes to 0V.
This allows node 2 to see the positive input voltage.
U4 then acts as a follower with a gain of +1 (applying the same voltage to the inputs of the opamp makes it act as a follower).
U6 is just a buffer for the RC glitch filter.

Thank you, so U5 and U4 basically make up a full wave rectifier? is there any benefit to using this topology for my application compared to the standard full wave rectifier circuit? Regards

 

so U5 and U4 basically make up a full wave rectifier?

No. They split the sawtooth into two halves and treat each half differently.

 

No. They split the sawtooth into two halves and treat each half differently.

So they are completely separate? this article from TI shows a similar circuit in figure 5, stating that it is a full wave rectifier? i am just trying to understand if this is the case, a possible reason to why it is preferred in this application

http://www.ti.com/lit/an/sboa068/sboa068.pdf

 

Providing the non-inverting input of the preamp gets clamped at half the peak voltage of the sawtooth during the lower half of the sawtooth only, then the circuit can be regarded as a full-wave rectifier or absolute value generator.

 

Providing the non-inverting input of the preamp gets clamped at half the peak voltage of the sawtooth during the lower half of the sawtooth only, then the circuit can be regarded as a full-wave rectifier or absolute value generator.

any benefits of this topology at all for this application ?

 

any benefits of this topology at all for this application ?

It may give a smaller glitch at the sawtooth flyback since U4's output does not have to change polarity when the input suddenly goes from a positive to negative input (or vice-versa).
My simulations have shown a higher output glitch for some of the other precision full-wave configurations.