-KtlpRLC _


We are interested in trying different values of Ck for the circuit; the other elements are already determined. Thus, we can let p take values ranging from zero (cathode resistor unbypassed) to infinity (resistor perfectly bypassed). Three special values of p are of interest.

-gmRL K

The time response for various values of p and for a particular value of K (approximately 2) is shown in Fig. 5-5. Notice that p = 1 gives a faster rise than does p = 0 and is the largest value of p that gives a monotonic rise (no overshoot); hence, this is the value usually chosen in the cathode-peak-

ing technique. Notice also that p = 100 is a value in the usual range of cathode bypassing; there is a fast rise—essentially that of the ideal case (p = co)—followed by a long-time sag as previously analyzed for the cathode bias circuit.

It would appear from a comparison of Eqs. (5-20) and (5-21) that cathode peaking with p = 1 gives a faster amplifier than does the perfectly

Fig. 5-5 Step response of the cathode-peaked circuit for different values of cathode capacitance. (Drawn for K = 2.)

bypassed case. Both responses are simple exponentials with a 10 to 90 per cent rise time already given in Eq. (4-3).

2.2 RhC

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