The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Mar. 15, 1977
Filed:
Nov. 28, 1975
Tom L Blackburn, San Jose, CA (US);
Otto G Wisotzky, San Francisco, CA (US);
GTE Automatic Electric Laboratories Incorporated, Northlake, IL (US);
Abstract
Gain control circuits associated with the base and emitter electrodes of a common-emitter transistor amplifier stage include pluralities of electrically conductive screw-type switches and resistors. The net gains provided by the associated gain control circuits are cumulative and determine the net gain of the stage. The gain changes provided by individual switches of the base and emitter gain control circuits are also cumulative, the switches being selectively closed in a prescribed manner to provide step changes in the decibel value of the net gain of the stage in discrete steps of the same magnitude. A plurality of transistor amplifiers with associated emitter gain control circuits may be connected in series, with the decibel values of voltage gains thereof also being additive, to provide additional steps and range of voltage gain. Series resistors in the base gain control circuit are selectively short-circuited by screw switches to decrease the input resistance of the amplifier stage. A bridging resistor is selectively connected across certain of the series resistors by one of these screw switches for causing the associated step change in the input impedance of the stage to be more nearly equal to the desired value. Resistors in the emitter gain control circuit are electrically connected in parallel with the emitter resistor in the AC circuit equivalent of the amplifier in various configurations by screw switches to decrease the effective emitter resistance and thereby increase the decibel value of amplifier gain in steps of prescribed magnitude. The emitter gain control circuit may be AC coupled to the emitter resistor and the emitter electrode of the amplifier. Alternatively, one side of this gain circuit may be directly electrically connected to the emitter electrode. A resistive voltage divider network is then connected to the other end of this gain control circuit and across the positive and negative terminals of a source of bias voltage. The network resistors are selected to provide the same DC bias voltage on both sides of the emitter gain control circuit. This prevents DC current flowing through the emitter gain control circuit as the resistance thereof is changed and thereby maintains the DC bias level on the transistor constant. In this manner, the effective emitter resistance, and thus the amplifier gain, may be changed to any desired value without changing the operating point of the amplifier.