Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Delay controlled switch
Reexamination Certificate
1998-01-21
2001-09-11
Ton, My-Trang Nu (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Gating
Delay controlled switch
C327S400000
Reexamination Certificate
active
06288592
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of data communications. More particularly, the invention relates to cable drivers, line drivers, wave shaping of digital pulses and rise and fall control circuits.
BACKGROUND OF THE INVENTION
The transmission of digital data along a transmission line may be accomplished using a cable driver. The cable driver receives the signal to be transmitted and generates a corresponding signal on the transmission line. One objective in the design of cable drivers is to maximize the rate at which data may be transmitted (the “data rate”) on the transmission line. Among other limitations, the maximum data rate which may be transmitted will be limited by two considerations:
i. The cable driver should not generate excessive electromagnetic radiation, which may affect the operation of other devices near the cable driver. To avoid electromagnetic radiation, the 20% to 80% rise and fall time of the low to high and high to low transitions of the output signal of the cable driver must not be less than a specified minimum rise/fall time. In the case of some cable drivers used in the motion picture and television industries, the Society of Motion Picture and Television Engineering (SMPTE) has set out a minimum rise/fall time of 400 pico-seconds (See SMPTE Standard 259M: 10-Bit 4:2:2 Component and f
SC
Composite Digital Signal Serial Digital Interface).
ii. The cable driver should minimize any jitter in its output signal by ensuring that the output signal is within a specified tolerance of its steady state level prior to the start of the next transition of the output signal.
Prior art cable drivers control the rise and fall times of the output signal with a resistor-capacitor circuit. Such circuits exhibit exponential low to high and high to low output transitions with the result that the output signal takes a relatively long time to settle within the specified tolerance to minimize jitter, while still having a sufficiently long 20% to 80% rise and fall time. Consequently, the data rate which can be transmitted by prior art cable drivers is limited.
BRIEF SUMMARY OF THE PRESENT INVENTION
The maximum data rate which can be transmitted may be increased by designing the cable driver to have linear low to high and high to low output transitions.
Accordingly, it is an objective of the present invention to provide an improved cable driver which has substantially linear low to high and high to low output transitions.
The primary feature of the improved cable driver is the ability to transmit data at higher data rates without increased jitter or electromagnetic radiation. In addition, the improved cable driver reduces the problems of ringing and overshoot in the output signal.
In one aspect, the improved cable driver comprises (a) an input port for receiving an input signal, comprising first and second input terminals; (b) an output port for transmitting an output signal on a transmission line, comprising first and second output terminals; (c) a first resistance and a second resistance for defining an output signal at said output port, said first resistance being coupled between a voltage source and said first output terminal and said second resistance being coupled between said voltage source and said second output terminal; (d) a plurality of switching stages, wherein each of said switching stages comprises a switch and a current source associated with said switch for producing a current, said current source being coupled to its associated switch and each of said switches being coupled to said output port; (e) a plurality of delay stages for providing a delay time, (f) one of said switching stages being coupled to said input port and the remaining switching stages being coupled in series, with a delay stage between at least some of successive pairs of said switching stages so that the rise and fall times of a selected portion of said output signal exceeds a selected duration.
In a second aspect, the improved cable driver comprises (a) an input port for receiving an input signal, comprising first and second input terminals; (b) an output port for transmitting an output signal on a transmission line, comprising first and second output terminals; (c) a first resistor and a second resistor for defining an output signal at said output terminal, said first resistor being coupled between a first voltage source and said first output terminal, and said second resistor being coupled between the first voltage source and said second output terminal, wherein the resistances of said first resistor and said second resistor are equal to the impedance of the transmission line; (d) a plurality of switching stages, wherein each of said switching stages comprises a switch and a current source associated with said switch for producing a current, said current source being coupled between its associated switch and a second voltage source, and each of said switches being coupled to said input port and being responsive to said input signal for coupling its associated current source to said first output terminal or said second output terminal and being capable of switching between said first output terminal and second output terminal with a specified switching time and wherein the switching time of each of said switches is equal; (e) a plurality of delay stages, such that the number of delay stages is one less than the number of switching stages, for providing a delay time, wherein each of said delay stages is coupled between a pair of said switches of said switching stages, for delaying the response of said switches to said input signal such that said switches operate in a sequential order and wherein the delay time of each of said delay stages is equal, and the delay time of said delay stages and the switching time of said switches are selected such that the output signal is substantially linear.
REFERENCES:
patent: 5107257 (1992-04-01), Fukuda
patent: 5355390 (1994-10-01), Yamamoto et al.
patent: 5446914 (1995-08-01), Paul et al.
patent: 5739707 (1998-04-01), Barraclough
patent: 0 518 625 A2 (1992-12-01), None
patent: 0 607 677 A2 (1994-07-01), None
patent: 0 664 515 A1 (1995-07-01), None
patent: 0 763 917 A2 (1997-03-01), None
patent: WO 92/17938 (1992-10-01), None
patent: WO 95/02926 (1995-01-01), None
Bereskin & Parr
Gennum Corporation
Nu Ton My-Trang
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