Analysis of a Broadband Detector Circuit

This paper presents a theoretical analysis of the steady-state behavior of an ideal linear detector with a broadband output circuit. Published analyses of a diode feeding a load resistance R1 shunted by a capacitance C1 show that detection efficiency D to the carrier frequency is a function of the ratio of R1 to the reactance of C1, or of R1C1 to 1/f, at the frequency of the applied signal, as well as of the ratio of R1 to the diode conduction resistance Rd. The broadband detector circuit considered here extends the range, at low values of R1/Xc1, over which D is maintained practically constant for values of R1/Rd less than ten. This constant carrier detection efficiency characteristic is realized by inserting the proper size inductance in the detector output circuit. The solution of the steady-state behavior of the broadband detector circuit is obtained by the method of successive approximations. As a first approximation, carrier detection efficiency is calculated for the case of an assumed infinite inductance in the output circuit. To obtain a practical solution, a second approximation is made for the case of a finite inductance in the detector output circuit. This solution is compared with the solution obtained with the assumed infinite inductance to obtain a safe minimum inductance value for any broadband detector design. Calculated data are presented for four values of the ratio R1/Rd.