I have been trying to build an ECL oscillator similar do the circuits described in the IQD crystal data book, by Winser and by Unruh (the latter two articles were on the ACG pages when they were still in service - what happenend to them?).
Basically, in this circuit the crystal is used in series resonant mode, it is connected from the non-inverting output to the non-inverting input, which in turn has a 15R load to AC ground. The rest is just for getting the DC setpoints right. The input is shorted to ground by the 15 R resistor for all frequencies except the series resonant mode where the crystal has nothing but its real impedance, which is around 10-20 R for HC-49 case devices.
As the 10216 ECL line receiver is not easily available, I used the single gate. 10H16 PECL line receiver. Apart from being faster (0.5 ns prop delay) which wouldn't hurt in this application, the chip is just the same.
Initially, the circuit would sometimes not start up, sometimes start up at the desired frequency, sometime start up in a spurious oscillation aroung 300-600 MHz. I tried various crystals, load resistors beween 10 and 39 R, loutput pull - downs between 100 and 200 R. No change.
The I found that the returns from the input and output loads had different vias to the ground plane just half an inch apart. I provided another wire bridge. The spurious oscillations were gone, but so was the fundamental oscillation. Even injecting a square wave signal couldn't humor the circuit into oscillation. Any ideas?
Frustated,
Eric
Basically, in this circuit the crystal is used in series resonant mode, it is connected from the non-inverting output to the non-inverting input, which in turn has a 15R load to AC ground. The rest is just for getting the DC setpoints right. The input is shorted to ground by the 15 R resistor for all frequencies except the series resonant mode where the crystal has nothing but its real impedance, which is around 10-20 R for HC-49 case devices.
As the 10216 ECL line receiver is not easily available, I used the single gate. 10H16 PECL line receiver. Apart from being faster (0.5 ns prop delay) which wouldn't hurt in this application, the chip is just the same.
Initially, the circuit would sometimes not start up, sometimes start up at the desired frequency, sometime start up in a spurious oscillation aroung 300-600 MHz. I tried various crystals, load resistors beween 10 and 39 R, loutput pull - downs between 100 and 200 R. No change.
The I found that the returns from the input and output loads had different vias to the ground plane just half an inch apart. I provided another wire bridge. The spurious oscillations were gone, but so was the fundamental oscillation. Even injecting a square wave signal couldn't humor the circuit into oscillation. Any ideas?
Frustated,
Eric