Circuit

摘要

1,168,907. Semi-conductor circuits. INTERNATIONAL BUSINESS MACHINES CORP. 6 Oct., 1967 [22 Dec., 1966], No. 45642/67. Heading H3T. [Also in Division H1] The electrodes of an elongated semi-conductor diode form the transmission lines of a directional coupler. A substrate 20 of, e.g. aluminium, provides a common return conductor for transmission lines 22, 23 coupled over a length L. Line 22 consists of a layer of gold separated from the substrate 20 by a layer 21 of insulant, e.g. SiO 2 . A layer 23 of N-type silicon, GaAs or InSb forms with the gold electrode 22 and ohmic electrode 24 (of e.g. aluminium) a Schottky-barrier diode which is back-biased to the non-conductive condition. Electrodes 22, 20 provide an input line, electrodes 24, 20 an output line, and electrodes 22, 24 a coupling line, the characteristic impedances of the three lines being respectively Z 1 , Z 2 and Zk. It is shown that, provided the coupling is weak, a directional effect is obtained if Z 1 Z 2 = Z2k, using as a criterion for directionality zero signal at one end of the output line. A further restriction is that the length L of the device must approximate to one-quarter wavelength at the working frequency. The Specification describes in detail how the various dimensions and electrical parameters may be adjusted to fulfil these conditions. Since the operation of the device depends crucially upon the capacitance of the diode, removal of the bias destroys the directionality. Thus, if a pulse from source Vp, Fig. 4, is applied to terminals E 1 , output signals appear at terminals A 1 , Eg so long as the voltage of the pulse remains below the bias voltage Vb. If the voltage peak of the pulse exceeds Vb, the diodes become conducting, directionality is destroyed and an output appears at terminals A 2 , this output signal being free from noise. Alternatively, the circuit may be used as a limiter by short-circuiting terminals A 2 and deriving an output from terminals A 1 . Only input voltages not exceeding Vb appear at the output.