Patent US3793480A successfully refreshed from Google Patents.
US3793480A
Expired / Lapsed
US
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Exponential transconductance multiplier and integrated video processor
Assignee: RTX Corp
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Filing: 1971-12-29
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Granted: 1974-02-19
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Expires: 1991-12-29
Abstract
Abstract A linear transconductance multiplier of the type having a pair of transistors connected in common emitter configuration to a source of tail current, and having each base of the transistors connected through respective diodes to another current source, is modified so as to provide an output (voltage or current) which is a function of a fractional exponent of the input (voltage or current) by placing a diode in series between each emitter and the tail current source. The diodes may be shunted by a switch so as to provide selectivity between linear and exponential functions, or the diodes may be partially shunted so as to adjust the exponential function between unity (linear) and the minimum exponent obtainable. Providing additional diodes in series with the transistor emitters decreases the exponent further. An integrated video processor comprises an exponential transconductance multiplier having differential inputs with contrast control provided by adjustment of the tail current, gamma correction being achieved automatically by the nonlinear function of the multiplier; the multiplier output is fed to a brightness-controlled, final amplifier.
Inventors
- 👤 G Waehner
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 05:02
CPC Classifications
H; H04; H04N; H04N5/00; H04N5/14; H04N5/20; H04N5/202; G; G06; G06G; G06G7/00; G06G7/12; G06G7/16; G06G7/24
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
143 words
In a transconductance multiplier of the type having the emitters of a pair of similar transistors connected to a common tail current source, and the bases of said pair of transistors connected through respective first diodes to a second common current source, said transistors having high beta yields and a base to emitter voltage which is a logrithmic function of the collector current therein, an output current comprising the collector current of one of the transistors being a function of the input current to the base of one of said transistors, the improvement comprising: a pair of second diodes, each connected between the emitter of each of said transistors and said common tail current source, whereby the output current is substantially a reciprocal exponential function of the input current; and a switch connected between said emitters for selectively short circuiting said second diodes.
Claim 2
Dependent Claim
143 words
In a transconductance multiplier of the type having the emitters of a pair of similar transistors connected to a common tail current source, and the bases of said pair of transistors connected through respective first diodes to a second common current source, said transistors having high beta yields and a base to emitter voltage which is a logrithmic function of the collector current therein, an output current comprising the collector current of one of the transistors being a function of the input current to the base of one of said transistors, the improvement comprising: a pair of second diodes, each connected between the emitter of each of said transistors and said common tail current source, whereby the output current is substantially a reciprocal exponential function of the input current; and a switch connected between said emitters for selectively short circuiting said second diodes.
Claim 3
Dependent Claim
36 words
A transconductance multiplier according to claim 1 wherein said tail current source is controlled by a manually operable contrast potentiometer, whereby the current in said source varies as a function of the setting of said potentiometer.
Claim 4
Dependent Claim
34 words
A transconductance multiplier according to claim 1 additionally comprising a variable impedance connected between said collectors for selectively shunting said diodes thereby to alter the relationship between the output current and the input current.
Claim 5
Dependent Claim
36 words
A transconductance multiplier according to claim 1 wherein said tail current source is controlled by a photosensor, whereby the current in said source increases as a function of ambient light in the vicinity of said photosensor.
Claim 6
Dependent Claim
34 words
A transconductance multiplier according to claim 4 including differential signal inputs, each connected to the base of one of said transistors, thereby to provide common mode noise rejection to signal inputs to said multiplier.
Claim 7
Dependent Claim
150 words
An integrated video processor for processing an input video signal for application to a CRT display, comprising: a transconductance multiplier having an output current which varies as the product of a tail current applied to said multiplier and roughly the square root of an input current to said multiplier, said multiplier having differential inputs; a tail current source supplying tail current to said multiplier, said tail current source being adjustable to vary the gain of said multiplier thereby to provide contrast control to said video processor; a brightness control providing an adjustable signal level corresponding to a desired display brightness; and a differential amplifier connected for response at one input to said brightness control and at another input to said multiplier, said differential amplifier providing a video output signal corresponding to the output of said multiplier level-adjusted about a reference potential in dependence upon the setting of said brightness control.
Claim 8
Dependent Claim
150 words
An integrated video processor for processing an input video signal for application to a CRT display, comprising: a transconductance multiplier having an output current which varies as the product of a tail current applied to said multiplier and roughly the square root of an input current to said multiplier, said multiplier having differential inputs; a tail current source supplying tail current to said multiplier, said tail current source being adjustable to vary the gain of said multiplier thereby to provide contrast control to said video processor; a brightness control providing an adjustable signal level corresponding to a desired display brightness; and a differential amplifier connected for response at one input to said brightness control and at another input to said multiplier, said differential amplifier providing a video output signal corresponding to the output of said multiplier level-adjusted about a reference potential in dependence upon the setting of said brightness control.
Claim 9
Dependent Claim
39 words
The integrated video processor according to claim 6 wherein said transconductance multiplier has an output current which varies as the product of the tail current applied to said multiplier and substantially the reciprocal 2.2 power of input current thereto.
Claim 10
Dependent Claim
40 words
The integrated video processor according to claim 6 wherein said tail current source comprises a photo sensor disposed to sense the ambient light level in the vicinity of the CRT display, thereby to automatically correct contrast as a function thereof.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-02-18 | 1977-08-20 | 1978-02-19 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-02-18 | 1981-08-20 | 1982-02-19 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-02-18 | 1985-08-20 | 1986-02-19 | $7700.00 | Window Closed / Lapsed |