Differential-input amplifier circuitry with increased common-mode _voltage range
First Claim
1. An amplifying circuit operable with input signals having a common-mode component anywhere within a range approaching and including at least one of the operating potentials applied to said amplifying circuit, in combination:
- first and second supply terminals for receiving operating potential therebetween;
first and second field-effect transistors of a first conductivity type, each having gate, drain, source and substrate electrodes;
means for connecting said first and second transistors in long-tailed-pair connection including first and second input terminals to which the respective gate electrodes of said first and second transistors connect for receiving input signals, a tail connection to which the respective source electrodes of said first and second transistors connect for receiving a tail current, first and second output connections to which the respective drain electrodes of said first and second transistors connect;
tail current supply means connected between said first supply terminal and said tail connection for supplying said tail current;
means for applying offsetting potentials between the respective substrate and source electrodes of both said first and second transistors, which offsetting potentials are of a polarity for maintaining the potential at the respective substrate electrodes of said first and second transistors closer to the potential at said first supply terminal than is the potential at the source electrodes of said first and second transistors, said offsetting potentials varying responsive to said common-mode component for tending to operate said first and second transistors towards depletion mode when the value of said common-mode component approaches the potential at said first supply terminal more closely than a predetermined voltage and tending to operate said first and second transistors towards enhancement mode when the value of said common-mode component departs from the potential at said first supply terminal by more than said predetermined voltage, said offsetting potentials conditioning said long-tailed pair connection for providing signals at its output connections responsive to said input signals when the common-mode component of said input signals is at a potential between the potentials at said first and second supply terminals and including at least the potential at one of said first and second supply terminals; and
differential to single-ended signal converting means including;
third and fourth transistors of a second conductivity type, having respective output electrodes connected respectively to the first and second output connections of said long-tailed-pair connection, having respective input electrodes, and having respective common electrodes connected to said second supply terminal,potential-follower means with an input connection at the output electrode of said third transistor and with an output connection at an interconnection between the respective input electrodes of said third and fourth transistors, which potential-follower means is for exhibiting a predetermined offsetting potential between its input and output connections to operate the output electrode of said third transistor at a potential between the potential at the input electrode of said third transistor and the potential at said second supply terminal including the potential at the input electrode of said third transistor, and,output means for operating the output electrode of said fourth transistor at a potential between the potential at the input electrode of said fourth transistor and the potential at said second supply terminal including the potential at the input electrode of said fourth transistor, and for supplying output signals related to the difference between the signals at the first and second output connections of said long-tailed-pair connection.
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Accused Products
Abstract
A differential-input amplifier suitable for the input stage of a CMOS operational amplifier has the capability of amplifying input signals with common-mode voltage components in a range including the entirety of its operating voltage. To provide this capability for one end of the common-mode range a long-tailed pair connection of depletion-mode field effect transistors with gates at the inverting and non-inverting input terminals of the amplifier is used; and to provide this capability for the other end of the common-mode range the substrates of the transistors are biased to operate them in effect as enhancement-mode transistors allowing their drains to work into a current mirror amplifier used for converting their balanced drain variations to single-ended form. Current mirror amplifier configurations are disclosed which are preferable for such conversion since they operate with reduced potential requirements, but are integrable in CMOS.
30 Citations
33 Claims
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1. An amplifying circuit operable with input signals having a common-mode component anywhere within a range approaching and including at least one of the operating potentials applied to said amplifying circuit, in combination:
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first and second supply terminals for receiving operating potential therebetween; first and second field-effect transistors of a first conductivity type, each having gate, drain, source and substrate electrodes; means for connecting said first and second transistors in long-tailed-pair connection including first and second input terminals to which the respective gate electrodes of said first and second transistors connect for receiving input signals, a tail connection to which the respective source electrodes of said first and second transistors connect for receiving a tail current, first and second output connections to which the respective drain electrodes of said first and second transistors connect; tail current supply means connected between said first supply terminal and said tail connection for supplying said tail current; means for applying offsetting potentials between the respective substrate and source electrodes of both said first and second transistors, which offsetting potentials are of a polarity for maintaining the potential at the respective substrate electrodes of said first and second transistors closer to the potential at said first supply terminal than is the potential at the source electrodes of said first and second transistors, said offsetting potentials varying responsive to said common-mode component for tending to operate said first and second transistors towards depletion mode when the value of said common-mode component approaches the potential at said first supply terminal more closely than a predetermined voltage and tending to operate said first and second transistors towards enhancement mode when the value of said common-mode component departs from the potential at said first supply terminal by more than said predetermined voltage, said offsetting potentials conditioning said long-tailed pair connection for providing signals at its output connections responsive to said input signals when the common-mode component of said input signals is at a potential between the potentials at said first and second supply terminals and including at least the potential at one of said first and second supply terminals; and differential to single-ended signal converting means including; third and fourth transistors of a second conductivity type, having respective output electrodes connected respectively to the first and second output connections of said long-tailed-pair connection, having respective input electrodes, and having respective common electrodes connected to said second supply terminal, potential-follower means with an input connection at the output electrode of said third transistor and with an output connection at an interconnection between the respective input electrodes of said third and fourth transistors, which potential-follower means is for exhibiting a predetermined offsetting potential between its input and output connections to operate the output electrode of said third transistor at a potential between the potential at the input electrode of said third transistor and the potential at said second supply terminal including the potential at the input electrode of said third transistor, and, output means for operating the output electrode of said fourth transistor at a potential between the potential at the input electrode of said fourth transistor and the potential at said second supply terminal including the potential at the input electrode of said fourth transistor, and for supplying output signals related to the difference between the signals at the first and second output connections of said long-tailed-pair connection. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A circuit for developing a voltage logarithmically related to the input current applied thereto, including
a first bipolar transistor having emitter and collector electrodes, and having a base electrode connected to a first node, means for applying a current between the collector and emitter electrodes of said first bipolar transistor, a direct-coupled feedback connection responsive to the potential at the collector electrode of said first bipolar transistor, of an improved type for maintaining the potential between the collector and base electrodes of said first bipolar transistor at some predetermined value, comprising: -
a first field-effect transistor of depletion-mode type, having a source electrode connected to said first node, having a gate electrode to which the collector electrode of said first bipolar transistor connects, and having a drain electrode connected for receiving a first operating potential; and constant current supplying means connected to the source electrode of said first field-effect transistor for supplying a substantially constant current thereto for biasing said first field-effect transistor for establishing said predetermined valued potential between the gate and source electrodes thereof. - View Dependent Claims (21, 22, 23, 24, 25)
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26. A current amplifier comprising:
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input, output, and common terminals; first and second transistors of the same conductivity type, each having respective output and common electrodes defining the ends of its principal current conduction path, and each having a respective input electrode, the potential between the common and input electrodes of each said transistor controlling the conduction of its principal current conduction path, their output electrodes connecting respectively to said input terminal and to said output terminal, and their common electrodes connecting to said common terminal; and means for maintaining the input electrodes of said first and second transistors at a potential respective to that at the output electrode of said first transistor and at least as remote from the potential at said common terminal, which means includes a third transistor of depletion-mode, field-effect type and of a conductivity type similar to that of said first and second transistors, having a gate electrode to which the output electrode of said first transistor connects, having a source electrode directly connected at the input electrodes of said first and second transistors, and having a drain electrode, and further includes means connected between the source and drain electrodes of said third transistor for supplying a substantially constant current to the source electrode of said third transistor to operate it as a source-follower amplifier exhibiting a predetermined potential between its gate and source electrodes. - View Dependent Claims (27, 28, 29)
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30. A current amplifier comprising:
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input, output and common terminals; first and second transistors of the same conductivity type, each having respective output and common electrodes defining the ends of its principal current conduction path, and each having a respective input electrode, the potential between the common and input electrodes of each said transistor controlling the conduction of its principal current conduction path, their output electrodes connecting respectively to said input terminal and to said output terminal, and their common electrodes connecting to said common terminal; and means for maintaining the input electrodes of said first and second transistors at a potential respective to that at the output electrode of said first transistor and at least as remote from the potential at said common terminal, which means includes; a third transistor of depletion-mode, field-effect type and of a conductivity type complementary to that of said first and second transistors, having a gate electrode to which the output electrode of said first transistor connects, having a source electrode directly connected at the input electrodes of said first and second transistors, and having a drain electrode, and further includes means connected between the source and drain electrodes of said third transistor for supplying a substantially constant current to the source electrode of said third transistor to operate it as a source-follower amplifier exhibiting a predetermined potential between its gate and source electrodes. - View Dependent Claims (31, 32, 33)
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Specification