I am working on a project that uses a 32.768kHz crystal to generate a signal. I need to keep it separated from another part of the overall circuit due to other oscillators being present (they tend to drive one another). In order to separate them, I have an optocouple/optoisolator between the two circuits which works fine at about the output of the oscillator in question. However, due to sensitivities later in the circuit, I need to clamp down on the voltage with a zener diode before the jump across the optocouple. To do this, i need to amplify my ~1.25VPP signal (0 to ~1.25V) to about 3VPP or so because I can't use a zener otherwise.
I've tried several amplification methods (inverting opamp, transistor, non-inverting opamp) but none of them are working well. The transistor amplifies to about 1.5VPP but no more. The inverting opamp boosts it to 3.5VPP but inverts it (not good for driving the LED in the optocouple). I couldn't get the non-inverting to work at all. I've tried two inverting opamps back to back also.
Is there a simple way to amplify the signal out of the oscillator to a level where i can clamp it and still drive the LED?
Diagram of the oscillator can be found here: http://www.eleccircuit.com/32768-khz-oscillator-using-a-watch-crystal/ (the one on the left side is the one I'm using. The inverter is fed with about 1.0-1.2VDC, and both caps are 22pf)
The optocouple is just an LED from the transmitting side.
Image of an optocouple: http://en.wikipedia.org/wiki/File:Optocoupler_Circuit.svg (the shaded box labeled D1 is the optocouple)
I've tried several amplification methods (inverting opamp, transistor, non-inverting opamp) but none of them are working well. The transistor amplifies to about 1.5VPP but no more. The inverting opamp boosts it to 3.5VPP but inverts it (not good for driving the LED in the optocouple). I couldn't get the non-inverting to work at all. I've tried two inverting opamps back to back also.
Is there a simple way to amplify the signal out of the oscillator to a level where i can clamp it and still drive the LED?
Diagram of the oscillator can be found here: http://www.eleccircuit.com/32768-khz-oscillator-using-a-watch-crystal/ (the one on the left side is the one I'm using. The inverter is fed with about 1.0-1.2VDC, and both caps are 22pf)
The optocouple is just an LED from the transmitting side.
Image of an optocouple: http://en.wikipedia.org/wiki/File:Optocoupler_Circuit.svg (the shaded box labeled D1 is the optocouple)