Perhaps I can do this in words, as I have no schematic software. Start with the input to your favorite microprocessor's A/D converter. Connect it to a suitable (more later) capacitor to analog ground. Connect a cmos switch across the cap and call it S2. When S2 is on, it discharges the cap.
Now build or buy a constant current generator connected from a suitable positive voltage to another cmos switch called S1. When S1 is on, all of the current generated flows to analog ground. To make it all work, connect the anode of a diode from the junction of the current source and S1 to the cap and analog input. When S1 is on, no current gets to the cap. When S1 is off, all of the current gets to the cap, if S2 is off. This causes a linear buildup of voltage across the cap, for a suitable time. When 1 PPS pulses are compared, suitable means one second to charge to almost the maximum that the micro A/D supports. The value of I is chosen to overwhelm diode leakage and A/D input current. The value of C follows. All that remains for a working system is a pair of flip-flops to control S1 and S2. FF 1 is set by PPS 1 and cleared by PPS 2, and by power on reset. When FF1 is on, S1 is off. FF 2 is set by PPS 1 and cleared by an output from the micro when the A/D conversion is done. When FF2 is on, S2 is off. And so C will charge from PPS 1 to PPS 2, hold the value while the A/D conversion occurs, and be reset to zero volts when the micro is done processing the input. This gives the micro a linear conversion of pulse difference time rather than an RC exponential value. Feedback controllers do better with linear error signals. But all of this is wasted if the PPS signals are not accurate due to things that affect pulse rise and fall times. If the above was not adequately clear, please ask for clarification. Or do a schematic and ask for corrections. Bill Hawkins P.S. This will not work well for small differences between PPS 1 and 2. It will work if the goal is 50% difference, or 90 degrees phase shift. -----Original Message----- From: Can Altineller Sent: Wednesday, September 23, 2015 2:56 AM --------%< ------ 4. I think an analog solution like Bill Hawkins described, would be best suited for this task. But I have not understood it enough to build it. Best Regards, C.A. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.