Xilinx Exhibit 1004
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`4,573,020
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`5
`which flows thru transistor 21. Transistor 21 functions
`as a current mirror input reference diode to mirror the
`reference current. or a portion thereof, to transistors 17
`and 19. The reference current is the sum of the currents
`flowing thru transistors 33 and 42 and is proportional to
`changes in the sum of the Output voltages at terminals
`24 and 28 with respect to the reference voltage V35.
`Transistor 27 functions as an output device which pro-
`vides the negative output voltage in proportion to the
`difference between the differential currents flowing
`thru transistors 16 and 18. Current source 26 is a bias
`current source which provides a bias current to transis-
`tor 27. Similarly. transistor 23 functions as a second
`output device which provides the positive output volt-
`age in proportion to the difference between the differ-
`ential currents flowing thru transistors 16 and 18. Cur-
`rent source 22 functions as a bias current source to
`provide a bias current to transistor 23.
`By now it should be apparent that a fully differential
`operational amplifier has been provided which provides
`a common-mode output voltage which is independent
`of the input common-mode voltage and is substantially
`independent of the differential input voltage variation.
`The differential amplifier utilizes D.C. feedback by
`using transistors 33, 35, 40, 42 and 21 to provide a pre-
`cise common-mode output voltage. The precise com-
`mou-mode output voltage is obtained without the use of
`timing signals and is size efficient for integrated circuit
`purposes.
`I claim:
`1. A fully differential operational amplifier compris~
`mg:
`current source means for providing a constant source
`current;
`first differential input means coupled to the current
`source means. for selectively receiving a first input
`voltage and providing a first differential current in
`proportion thereto;
`second differential input means coupled to the cur-
`rent source means, for selectively receiving a sec-
`oud input voltage and providing a second differen-
`tial current in proportion thereto;
`first current sink means coupled to the first differen-
`tial input means, for sinking said first differential
`current in proportion to a reference current;
`second current sink means coupled to the second
`differential input means, for sinking said secoud
`differential current in prOportion to the reference
`current;
`first output means coupled to the first current sink
`means, for providing a first output voltage at a first
`output
`terminal
`in preportion to the difference
`between the first and second differential currents;
`second output means coupled to the second current
`sink means, for providing a second output voltage
`at a second output terminal in proportion to the
`difference between the first and second differential
`currents; and
`common mode feedback means coupled to the first
`and second current sink means for providing the
`reference current in prOportion to changes in the
`sum of the first and second output voltages relative
`to a reference voltage.
`2. The fully differential operational atoplifier of claim
`1 further comprising:
`second current source means coupled to the first and
`second output terminals, for supplying current to
`said first and second output means.
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`3. A fully differential operational amplifier compris-
`mg:
`first current source means for providing a first con-
`stant current;
`first differential input means coupled to the first cur-
`rent source means, for selectively receiving a first
`input voltage and providing a first differential cur-
`rent in proportiOn thereto;
`secoud differential input means coupled to the first
`current source means, for selectively receiving a
`second input voltage and providing a second differ—
`ential current in proportion thereto;
`first current sink means coupled to the first differen-
`tial input means, for sinking said first differential
`current in proportioa to a reference current;
`seccmd current sink means coupled to the second
`differential
`input means, for sinking said second
`differential current in proportion to the reference
`current;
`first output means coupled to the first current sink
`means, for providing a first output voltage at a first
`output
`terminal
`in proportion to the difference
`between the first and second differential currents;
`second output means coupled to the second current
`sink means, for providing a second output voltage
`at a second output terminal in proportion to the
`difference between the first and second differential
`currents;
`a second current source for supplying a second con-
`stant current;
`a third current source for supplying a third constant
`current;
`a first transistor having a first current electrode cou-
`pled to the secOnd current source, a control elec-
`trode ccmnected to the first output terminal, and a
`second current electrode connected to the first
`current sink means;
`a second transistor having a first current electrode
`connected to the second current source. a control
`electrode connected to the reference voltage, and a
`second current electrode connected to a power
`supply terminal;
`a third transistor having a first current electrode con-
`nected to the third current source, a control elec-
`trode connected to the reference voltage, and a
`second current electrode connected to the power
`supply terminal;
`a fourth transistor having a first current electrode
`connected to the first current electrode of the third
`transistor, a control electrode connected to the
`second output terminal, and a second current elec-
`trode connected to the second current sink means.
`said first and fourth transistors providing the refer-
`ence current; and
`current mirror means coupled between the second
`current electrode of the first and fourth transistors
`and the power supply terminal, for mirroring a
`predetermined portion of the reference current to
`the first and second current sink means.
`4. A fully differential operational amplifier compris-
`mg:
`first, second and third current source means for pro-
`viding first, second and third constant source cur-
`rents;
`a first transistor coupled to the second current source
`means, for selectively receiving a first input volt—
`age and pr0viding a first current
`in proportion
`thereto;
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