Miller negative resistance Oscillator
@7/23, 2015
even though i build several times the miller style oscillator, but i always wonder how it works, even in a very basic level.
Miller style Overtone oscillator
Note: and if it did not get a reliable start, a capacitor from T1 collector to base might needed(if high Ft of transistor and low oscillate frequency.
( C2 is need some time)
What is Miller?
<< Practical Oscillator Handbook>> by Irving M. Gottlieb introduce the miller:
In the tuned-output/tuned-input oscillator, the transistor exhibits a 'Miller' effect; that is, its input acts as a negative resistance
when the output tank is tuned to appear inductive at the parallel-resonant frequency of the emitter-base tank (lower frequency
than base tank).
Improvement suggested by << Practical Oscillator Handbook>>
* A, radio frequency choke in bias circuit makes for easier starting. reduce bias shunting effect.
* B, C, D, E, Resistors(10-20R) and~or ferrite beads discouraged high frequency parasitics.
* F Tapped tank inductor can optimize impedance match to transistor.
* G, Collector radio frequency choke should be a different value from base-circuit choke A.
* H, I, J, Decoupling network discourages low frequency parasites.
* K, Faraday shield helps isolate oscillator from load
At higher power levels the collector circuit of the transistor tends to load down the parallel-tuned tank, A tap F, rescu this from BJT.
Miller oscillator from <EMRFD>
Miller type oscillator tend to output much power. 10-20mW typically. one can say this is a Colpitts type oscillator while the C3 is omit(except 1Mhz or 3Mhz).