Diode Detection Analysis

This paper gives the current and output relations for the linear and square-law diode detector in terms of the detection efficiency and the detector and load resistances. The square-law case is shown to yield results similar to the linear for large input potentials and reasonable values of load. Employing the rectification-current-input-voltage characteristic, the graphical method is used to show that serious distortion is developed for deep modulation whenever an appreciable audio load is shunted across the diode resistor. It is found that M = 1 + D(A-1), where M is the modulation ratio at which cut-off begins, D the detection efficiency, and A the ratio of the audio impedance to the direct-current value of the diode load. The value of M is shown for various load conditions in both the linear and square-law cases. The paper shows that the use of a small condenser across the load decreases the detection efficiency but increases the input impedance. The connection to the driving circuit of a second diode for the development of automatic volume control potential is shown to cause distortion when such a tube is used with a delay bias. Mention is made of the importance of considering the impedance of the driving circuit, and attention is called to the failure of any of the methods of analysis to consider all of the factors involved.