The oscillator does not switch off at the same voltage

[jmvinay1]

Hi,

I have designed quite a few cross coupled oscillators(on board) which show some hysteresis. Say, circuit draws current at 1.4V and starts oscillating. If I start decreasing the voltage from that point, circuit does not turn off at the same voltage(1.4V). Instead, it draws current and keeps oscillating up to 1 V. Is it a behavior of all oscillators? If not, what could be the problem with my circuit?

Thank you,
Vinay

 

[BigBoss]

It's normal..
Since the oscillation conditions are satisfied, the oscillator will continue to oscillate.But if you apply 1V instead of 1.4, the oscillator may not start to oscillate because oscillation and start-up conditions are different.( it may also start to oscillate, it was just a remark)

 

[jmvinay1]

Correct. Thank you. Device(used in oscillator) turn on voltage itself is 1.4V. According to your explanation, the device turn on at 1.4V and since it is oscillating, swing of the oscillation would turn on the device, even if the DC applied voltage is 1V. Is this the correct explanation?

 

[BigBoss]

Correct. Thank you. Device(used in oscillator) turn on voltage itself is 1.4V. According to your explanation, the device turn on at 1.4V and since it is oscillating, swing of the oscillation would turn on the device, even if the DC applied voltage is 1V. Is this the correct explanation?

There isn't any definition called as "turn-on" or "turn-off".There are just the convenient conditions to start-up or to maintain the oscillations.
Sometimes the start-up condition may have negative hystherisis-for instance a Colpitts oscillator may start-up to oscillate with low collector/drain current compare to higher current.Oscillator circuits are really interesting and pretty nonlinear/stochastic systems.It's really tough to understand by linear approximations/considerations.

Your case looks like the problem start-up and maintain/hold-on behaviour therefore it's normal..

 

[jmvinay1]

Thank you,

Sorry,
I did not mean the oscillator turning on when i said device turn on. If i use the same transistor as an amplifier, the device turns on at 1.4V and turns off if i decrease the voltage less than 1.4V.