Electronic apparatus for biological research Electronic apparatus for biological research . electronicappara00dona Year: 1958 INTERSTAGE COUPLINGS capacitance is low due to the substantial suppression of Miller effect. (2) is a much greater effect than (1), and as F^ has itself to be coupled to a source possessing internal resistance ampHfiers often employ pentodes throughout. With direct coupled amphfiers the equivalent circuits at high frequencies are similar, the climbing and neon-coupled types performing best. With couphng batteries the upper cut-off frequency is liable to be somewhat low
Electronic apparatus for biological research Electronic apparatus for biological research . electronicappara00dona Year: 1958 INTERSTAGE COUPLINGS capacitance is low due to the substantial suppression of Miller effect. (2) is a much greater effect than (1), and as F^ has itself to be coupled to a source possessing internal resistance ampHfiers often employ pentodes throughout. With direct coupled amphfiers the equivalent circuits at high frequencies are similar, the climbing and neon-coupled types performing best. With couphng batteries the upper cut-off frequency is liable to be somewhat low because of the stray capacitance of the bulky battery to earth. The potential divider type requires rather more comment. Referring back to Figure but assuming Fj and V^ to be pentodes, the equivalent circuit at high frequencies is Figure Sectioning the circuit along the dashed line and applying ffm<SK Vc grid n->-A)Cga Figure Rl r, fl^/-'''*^- ââ1^2 9'''^ ^2 -L Cs*Cg^*(uA)C, â go ir^ Figure HT+ HT* ^ n^C, <R S^2 HT- Figure Thevenin's theorem to the part to the left, we get Figure Clearly sinceâ as we have seenâR^ and R^, have to be made much larger than Rj^ the source resistance is higher than in the other systems and the upper cut-off frequency will be correspondingly low. The solution is to connect a compensating capacitance Cq across R^ as in Figure Lumping V^ input capacitances together as Cm, the equivalent 156
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