Colpitts 6Mhz PUBLIC

Trying to match a CL schematic with a real circuit build.

>Guidance only - simulation is very sensitive to values of R3 and Time Domain step<

>Q1 base current reverses quickly - is this realistic?<

Power

Simulated

Q1 seems to dissipate about 1.3mW as part of (not fully identified) mechanism to keep the oscillations going. No ideas yet about what can be measured in practice.

Energy into C1 tank (suspect calc?) is 660pJ in 170nS period > 3.9mW; dissipation in R3 (DC) 4.7mW (R3 AC = ?); R1+R2 4mW; Battery supplies 11mW

1.3 + 3.9 + 4.7 + 4 = 13.9, which is mediocre agreement between figures (should re-check...)

Real (yet to be measured)

Tank Sim freq ~=6Mhz; V(collector) about 5.75v p-p.

There is a 5uS ripple on base and C1 currents - cause?

Charge +ve/-ve here refers to the AC operation of C1. The absolute charge on C1 remains positive, but varying.

+ve current into C1 delivers a charge (fromL1) of about 676pC over a half cycle of the tank. As a first approx reading, during the -ve half cycle, about -498pC is part of the tank and -166pC is controlled by Q1 collector. Looking more closely at this -ve current half, a charge of 2.6mAx18.2nS = 47pC needs to be reallocated. A more accurate split of -ve dynamic charge would be 545/119pC tank/Q1-collector.

Energy (suspect calc?) loss/replenishment rate: 119pC from 110pF means a voltage change of about 1volt, -2 to -3v. Energy = 275pJ, rate of supply: 275pJ/170nS = 1.6mW (3.9mW by other method).

Base Current What causes the very fast - 15nS - reversal of base current, coincident with peak collector current? Realistic?

Real cct notes

Coil L1 is loosely (= untidily!) wound - theoretically = 8uH; sim suggests nearer 6uH. Details 15 turns, air core, loosely wound, so very roughly: dia 8mm, length 8mm, depth 5mm.

Q1 is BC109, beta 280.

Freq is close to 6MHz; Collector voltage approx 1.2v p-p - but variable measurements.

Battery supplies 1.35mA @ 8.88v = 12mW. Power calc from sim about losses in tank is probably indicative of real cct.