Crystal Oscillators

Oscillators with Crystals Having Two Sets of Electrodes

The original crystal oscillator devised by Dr. Nicolson, as well as a number of the earlier crystal oscillators tested by Dr. Cady, employed crystals with, effectively, two pairs of electrodes. The basic circuit is shown in figure 1-156. The re quired phase inversion of, the amplifier output voltage is provided by the crystal unit operating at a mode for which the polarities of the plate and grid terminals with respect to ground are 180 degrees out of phase. The circuit shown operates the crystal unit very

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Miller Oscillator with Cricuit

1428. The Miller oscillator is the crystal equivalent of a Hartley oscillator in which no mutual inductance exists between the plate-to cathode and gridt o.cithode inductances. ( See figure 1-140.) The Miller oscillator has an average frequency deviation of approximately 1.5 times that of the Pierce circuit. The plate circuit must appear inductive in order that the correct phase shift will be produced in E, the plate r-f voltage, to compensate for the

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Static Capacitor Exciter Stand-Alone IG for Pumping Systems

Bearing in mind the energy storage capacity or water pumping in a reservoir for later use appears to be the most appropriate ways to employ wind energy, which has a supply that depends on time, by day & season. As variable speed is useful, to tap most of the wind energy from cut-in to cut-off wind speeds, the frequency of the voltage produced by the IG varies noticeably, however the ratio V/f does not vary as that much. For induction-motor-driven pumps, such a situation is satisfactory.

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SWITCHED CAPACITOR FILTERS

The principle circuit of a switched capacitor filter has been demonstrated in the figure 25.5 shown below The basic low-pass filter is made up of 2 capacitors, along with CMOS switches that are turned on alternately by a built-in clock oscillator. The clock runs at more than a few tens of kilohertz.

The switch C1 samples the input voltage when the 1st switch is closed & the 2nd switch is open. This voltage may be +ve or -ve depending on the phase of the input signal at that instant. An instant later the switches change state & the charge on C1 is equalized with the charge on C2, which came from the preceding sampling.

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COMMON-COLLECTOR AMPLIFIER

The common-collector amplifier shown below contains an emitter resistor but the collector is connected directly to the positive rail. The base is biased by 2 resistors. Supposing that

·       the quiescent emitter current is about 1 mA,

·       the voltage present across the emitter-resistor R3 is 7.5 Volt,

·        bringing the output to exactly half-way between the supply rails.

·       To provide for a vBE of 0.7 V, it needs to hold base at 8.2 V.

·       The values of R1 and R2are calculated to provide this.

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