Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver
Reexamination Certificate
2000-08-25
2003-04-22
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Current driver
C327S595000, C307S036000, C307S077000
Reexamination Certificate
active
06552581
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of circuits and, more particularly, to a method and apparatus for current recycling for circuits.
BACKGROUND OF THE INVENTION
Current steering is gaining high visibility as a vehicle for high speed data transfer. The constant need to transfer more information faster, accompanied by increases in data processing capability has necessitated an expansion to data transfer rates considerably higher than what was previously possible. One data transmission scheme used to accomplish these higher rates is differential data transmission in which the difference in voltage levels between two signal lines form the transmitted signal. Differential data transmission is commonly used for data transmission rates greater than 100 Mbps and over long distances. Noise signals in the differential transmission shift the ground level voltage and appear as common mode voltages. Thus, the deleterious effects of noise are substantially reduced.
An example of a conventional low voltage differential swing (LVDS) driver circuit
800
used for differential data transmission is shown in FIG.
10
. The difference in voltage between the output signals OUT+, OUT− on the output terminals
803
,
805
form a pair of differential signals. A pair of differential signals, means two signals whose current waveforms are out of phase with one another. The individual signals of a pair of differential signals are indicated by reference symbols respectively ending with “+” and “−” notation (e.g., S+and S−). The composite notation “+/−” is employed to indicate both differential signals using a single reference symbol, e.g., S+/−.
The LVDS driver circuit
800
includes a direct current (DC) constant current source I
1
coupled to voltage supply VDD, four n-channel metal oxide semiconductor (NMOS) switches M
11
-M
14
, and a resistor R
1
coupled between the common node COM and voltage supply VSS. The four transistor switches M
11
-M
14
are controlled by input voltage signals VIN
1
, VIN
2
and direct current through load resistor Rt as indicated by arrows A and B. The input voltage signals VIN
1
, VIN
2
are typically rail-to-rail voltage swings. The gates of NMOS switches M
11
and M
14
couple together to receive input voltage signal VIN
1
. Similarly, the gates of NMOS switches M
12
and M
13
couple together to receive input voltage signal VIN
2
.
Operation of the LVDS driver circuit
800
is explained as follows. Two of the four NMOS switches M
1
-M
14
turn on at a time to steer current from current source I
1
to generate a voltage across resistive load Rt. To steer current through resistive load Rt in the direction indicated by arrow B, input signal VIN
2
goes high turning ON NMOS switches M
12
and M
13
. When input signal VIN
2
goes high, input signal VIN
1
goes low to keep NMOS switches M
11
and M
14
OFF during the time NMOS switches M
12
and M
13
are ON. Conversely, to steer current through resistive load Rt in the direction indicated by arrow A, input signal VIN
1
goes high and is applied to transistor switches M
11
and M
14
to make them conduct. Input signal VIN
2
goes low to keep NMOS switches M
12
and M
13
OFF during this time. As a result, a full differential output voltage swing can be achieved.
In other words, the prior differential LVDS driver circuit
800
sources current from VDD and sinks this current to VSS. In between, a switching array controlled by a Boolean signal routes the source current through the interconnect to an external resistive load. The return current is routed back to the array and sunk to VSS. The polarity of the voltage drop across the resistor carries the digital value. Changing the polarity of the array causes the current to route through the interconnect and resistor in the opposite direction and transfer the other digital value.
In addition to the requirement for transferring data at greater speeds, there is continuous pressure to reduce the amount of power consumed by integrated circuits. The differential LVDS offers reduced power consumption as compared with other drivers. The disadvantage is the need to have a set of interconnects for each signal because a differential LVDS driver is provided for each of the interconnects. It is this need to have a set of interconnects for each signal that drives the power of an integrated circuit using differential LVDS driver circuits. Thus, it would be desirable to provide a means to implement the differential LVDS driver circuits at a lower power.
SUMMARY OF THE INVENTION
The present invention is directed to a process and circuitry for drawing current from a power source to produce a first operation, such as a Boolean operation, and reusing the current to generate a further operation. In other words, the current from the first operation may be used to perform a second or subsequent operation instead of sinking the current to ground or another power source. This process is referred generally herein as current recycling.
REFERENCES:
patent: 5032745 (1991-07-01), Izadinia et al.
patent: 5130580 (1992-07-01), Min et al.
patent: 5202618 (1993-04-01), Nishimura
patent: 5574344 (1996-11-01), Matsuoka et al.
patent: 5708389 (1998-01-01), Gabara
patent: 5734272 (1998-03-01), Belot et al.
patent: 5867057 (1999-02-01), Hsu et al.
patent: 5909128 (1999-06-01), Maeda
patent: 5977796 (1999-11-01), Gabara
patent: 6154044 (2000-11-01), Herr
patent: 58210722 (1983-08-01), None
Agere Systems Inc.
Callahan Timothy P.
Englund Terry L.
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