Transformerless current balanced amplifier

• US 4,586,000 A
• Filed: 06/15/1984
• Issued: 04/29/1986
• Est. Priority Date: 02/10/1982
• Status: Expired due to Term

• Current Assignee: Space Systems/Loral Incorporated (Loral Space and Communications Incorporated)
• Original Assignee: Ford Aerospace & Communications Corporation (Galileo Parent, Inc.)
• Inventors: Wagner, Gary L.
• Primary Examiner(s): LaRoche, Eugene R.
• Assistant Examiner(s): Mottola, Steven J.
• Application Number:
  US06/621,014
• Time in Patent Office: 683 Days
• Field of Search: 330/252, 330/253, 330/254, 330/257, 330/261, 330/300, 330/301
• US Class Current: 330/252
• CPC Class Codes: H03F 2203/45376 the AAC comprising one or more discrete resistors as shunts between collectors or drains
• CPC Class Codes: H03F 2203/45392 the AAC comprising resistors in the source circuit of the AAC before the common source coupling
• CPC Class Codes: H03F 2203/45458 the CSC comprising one or more capacitors
• CPC Class Codes: H03F 2203/45496 the CSC comprising one or more extra resistors
• CPC Class Codes: H03F 2203/45594 the IC comprising one or more resistors, which are not biasing resistor
• CPC Class Codes: H03F 2203/45631 the LC comprising one or more capacitors, e.g. coupling capacitors
• CPC Class Codes: H03F 2203/45691 the LC comprising one or more transistors as active loading resistors
• CPC Class Codes: H03F 2203/45694 the LC comprising more than one shunting resistor
• CPC Class Codes: H03F 2203/45696 the LC comprising more than two resistors
• CPC Class Codes: H03F 3/3044 Junction FET SEPP output stages H03F3/3008 takes precedence
• CPC Class Codes: H03F 3/4508 using bipolar transistors as the active amplifying circuit H03F3/45278 takes precedence
• CPC Class Codes: H03F 3/45085 Long tailed pairs H03F3/45112, H03F3/45139 take precedence
• CPC Class Codes: H03F 3/45376 using junction FET transistors as the active amplifying circuit H03F3/45278 takes precedence

Abstract

A current balanced linear amplifier which does not contain a transformer. A differential transistor pair (22, 32) forms the amplifying element, with at least one transistor (22 or 32) having an input signal (71, 72) applied to its base. A current sink (52) sinking a fixed value of current (I) is coupled to the commonly-coupled emitters of the transistor pair (22, 32). Coupled to the collector of each amplifying transistor (22, 32) is a self-biasing constant current source (2, 12) which produces a fixed amount of current (I/2) equal to one half the current (I) sunk by the current sink (52). Each self-biasing constant current source (2, 12) comprises a field effect transistor (2, 12) having a capacitor (6, 16) connected between the gate G and source S of the FET (2, 12) in a positive feedback arrangement. The balanced current output (61, 62) is taken from the collectors of each of the two amplifying transistors (22, 32).

Claims

1. A transformerless current balanced linear amplifier for amplifying input signals, said amplifier operable over a wide a.c. frequency range of input signals and comprising:

first and second amplifying transistors connected as a differential pair, each transistor having a base, a collector, and an emitter, with at least one of said transistors having an input signal applied to its base;

first and second output terminals having a current balanced output therebetween, the collector of the first transistor being a.c. coupled to the first output terminal and the collector of the second transistor being a.c. coupled to the second output terminal;

a first self-biasing constant current source coupled to the collector of the first transistor; and

a second self-biasing constant current source coupled to the collector of the second transistor;

wherein each self-biasing constant current source comprises a field effect transistor having a gate, a source, and a drain; and

a capacitor connects together the gate and the source of each field effect transistor, whereby each self-biasing constant current source produces a fixed amount of current across the a.c. input signal frequency range of the amplifier, but acts as a constant voltage source for d.c. input signals.