Complementary field effect transistor differential amplifier
AssigneeRCA Corporation
InventorRichard Lee Pryor
Life of this patent
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Abstract
A feedback circuit responsive to the output signals of two amplifiers provides feedback in a sense to amplify differential mode components and reject common mode components of input signals supplied to the amplifiers, the resultant common mode rejection ratio (CMRR) being substantially independent of the magnitude of the common mode voltage. A further feedback circuit provides feedback of a sense to increase the CMRR when the magnitude of the common mode voltage differs in either sense from a given value whereby the net CMRR increases from a minimum value as the common mode voltage varies in either sense from the given value.
Claims7
In a complementary field effect transistor differential amplifier of the kind having two input terminals for receiving input signals, each signal including a common mode voltage component, V.sub.cm, two output terminals for providing output signals and two internal nodes at different voltages, said node voltages each changing in the same sense for a given change in V.sub.cm, the improvement, comprising:
- a pair of inverting amplifiers having the input and output terminals thereof cross-coupled between said two output terminals, each inverting amplifier receiving operating voltages from said nodes, each amplifier having a gain, the product of said gains being not greater than unity, said inverting amplifiers for supplying current to both of said two output terminals from one of said nodes when V.sub.cm is greater than a given value and for withdrawing current from both of said two output terminals via the other of said nodes when V.sub.cm is less than said given value.
In a differential amplifier of the kind comprising first and second nodes;
- first and second complementary field effect transistor amplifiers, each amplifier having a first operating voltage terminal connected to said first node, a second operating voltage terminal connected to said second node, an input terminal and an output terminal;
- a first variable impedance circuit coupled between said first node and a first reference voltage terminal;
- a second variable impedance circuit coupled between said second node and a second reference voltage terminal;
- and means coupling each output terminal to a separate control terminal of each variable impedance circuit, the improvement, comprising:
- a pair of inverting amplifiers cross-coupled between said output terminals of said first and second amplifiers, each inverting amplifier receiving operating voltages from said nodes, said pair of inverting amplifiers having a gain product not greater than unity.
In combination:
- first and second nodes;
- first and second complementary field effect transistor amplifiers, each having a first operating voltage terminal connected to said first node, a second operating voltage terminal connected to said second node, an input terminal and an output terminal;
- a first variable impedance circuit coupled between said first node and a first reference voltage terminal and a second variable impedance circuit coupled between said second node and a second reference voltage terminal, each variable impedance circuit having a first control electrode coupled to the output terminal of the first amplifier and a second control electrode coupled to the output terminal of the second amplifier;
- and
- third and fourth complementary field effect transistor amplifiers, each having a first operating voltage terminal connected to said first node, a second operating voltage terminal connected to said second node, an input terminal and an output terminal, the input terminal of the third amplifier being connected to the output terminals of the first and fourth amplifiers, the input terminal of the fourth amplifier being connected to the output terminals of the second and third amplifiers, said third and fourth amplifiers each having a gain which is not greater than unity.
Dependencies are inferred from the claim text.