Electronic apparatus for biological research Electronic apparatus for biological research . electronicappara00dona Year: 1958 DIODE CIRCUITS with respect to earth by an amount — V. When the circuit is in equihbrium there is a steady potential difference F/2 across the capacitance and diode current flows only at the very positive peaks of the signal, just enough to replace the charge lost by current flowing back round the circuit consisting of resistance and generator. SHUNT DIODE SIGNAL RECTIFIER The shunt diode signal rectifier circuit (Figure ) has a rather peculiar performance which mi
Electronic apparatus for biological research Electronic apparatus for biological research . electronicappara00dona Year: 1958 DIODE CIRCUITS with respect to earth by an amount — V. When the circuit is in equihbrium there is a steady potential difference F/2 across the capacitance and diode current flows only at the very positive peaks of the signal, just enough to replace the charge lost by current flowing back round the circuit consisting of resistance and generator. SHUNT DIODE SIGNAL RECTIFIER The shunt diode signal rectifier circuit (Figure ) has a rather peculiar performance which might lead one to wonder why anyone should want to use it. Its output is a rectified version of the input modulated carrier wave plus the Figure modulated carrier wave itself, and usually has to undergo further filtration to remove this carrier component. The reason for its appearance is as follows: many pentode and triode valves include—for a particular purpose in radio receivers—one or two thermionic diodes. These diodes share the same cathode as the main valve and are at a fixed potential. They therefore cannot be used for signal rectification of the series diode type—where both electrodes are 'live'—but are suitable for shunt rectification where one side of the diode is earthed. PHASE-SENSITIVE DETECTORS The function of these valuable devices is perhaps best illustrated by an example: In recent work F. W. Campbell and W. A. H. Rushton (/. Physiol. 130 (1955) 131) have studied the absorption of light by the retina of the eye. To do this, a red and a green beam of light were directed into the eye alternately. The emergent reflected hght, which has twice passed through the visual purple, was coflected by a photocell. If the amount of visual purple changed, the brightness of the green beam altered with respect to the red. By adjusting a purple wedge (in the path of the green beam) these intensities could be matched {Figure ). The photocell output is a square w
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