. Electronic apparatus for biological research . |—T-AAAWV^ Output Figure 39. J 7 where the amplifier is a simple two-stage affair using a double triode. The relay moving contact 'buzzes' back and forth between the fixed contacts, alternately earthing the input and the output. The periodic short-circuiting of the input converts it into a square wave of amplitude proportional to flftntin ""mm (a) (b) Figure itself and of phase depending on its polarity. This emerges from the ampli- fier about a thousand times greater and is phase-sensitive-rectified by the other relay contact in
. Electronic apparatus for biological research . |—T-AAAWV^ Output Figure 39. J 7 where the amplifier is a simple two-stage affair using a double triode. The relay moving contact 'buzzes' back and forth between the fixed contacts, alternately earthing the input and the output. The periodic short-circuiting of the input converts it into a square wave of amplitude proportional to flftntin ""mm (a) (b) Figure itself and of phase depending on its polarity. This emerges from the ampli- fier about a thousand times greater and is phase-sensitive-rectified by the other relay contact in a manner similar to the Cowan bridge described in Part I. The output is now of the form shown in Figure , and if this is filtered it has the appearance of Figure and is a magnified copy of the input. The chopping frequency should be the highest at which the relay will work properly, and the filter can then be designed to cut off at, say, one-third of this, and the amplifier will then handle input frequencies up to, say again, one-tenth. A difficulty with chopper amplification of this rudimentary type is this: 630
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