Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Amplitude control
Reexamination Certificate
2001-07-19
2003-05-06
Le, Dinh T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Amplitude control
C327S108000, C327S262000
Reexamination Certificate
active
06559702
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to bias generator circuits, and more particularly to a bias generator circuit architecture and method that protects output skew voltage capabilities for an associated output circuit.
2. Description of the Prior Art
Known bias generator circuits are problematic in that they generate bias voltages to their associated output circuits that are inordinately sensitive to process, temperature and supply voltage variations, thereby limiting overall circuit performance capabilities. When the process is strong, temperature is low and supply voltage is at the maximum level, the output low-to-high and high-to-low propagation delays associated with an output circuit that is biased via the bias generator circuit are at their fastest. When the process is weak, temperature is high and supply voltage is at the minimum level, the output low-to-high and high-to-low propagation delays associated with an output circuit that is biased via the bias generator circuit are at their slowest.
FIG. 1A
is a schematic diagram illustrating a known output voltage bias generator
10
that supplies different voltage levels (biasp
12
and biasn
14
) to an output circuit
100
illustrated in
FIG. 1B
, wherein the different voltage levels are sensitive to variations in the process, ambient and operating temperatures, supply voltage and resistor tolerance. The bias generator
10
in combination with output circuit
100
promotes tight low-to-high and high-to-low output skews over the variation of operating conditions.
When the process is strong, temperature is low and supply voltage is at the maximum level (herein referred to as the first operating condition), the biasp
12
level is at a higher voltage level and the biasn
14
level is at a lower voltage level than they would otherwise be when the process is weak, temperature is high and supply voltage is at its minimum level (herein after referred to as the second condition). During a first condition situation therefore, the biasp
12
and biasn
14
voltage levels are closer to the thresholds of the skew adjusting devices MNSKEW
1
(
102
) and MNSKEW
2
(
104
), and will weaken the skew adjusting devices
102
,
104
. This will slow down the low-to-high and high-to-low propagation delays, pushing the skew closer to the second operating condition.
During a second condition situation, the biasp
12
level is at a lower voltage level than it would otherwise be during a first condition situation; and the biasn
14
level is at a higher voltage level than it would be during a first condition situation. During a second condition situation therefore, the biasp
12
and biasn
14
voltage levels “turn on” the skew adjusting devices
102
,
104
harder than during a first condition situation, and will not weaken the skew adjusting devices
102
,
104
as much as that caused during a first condition situation. The foregoing described varying voltage levels for biasp
12
and biasn
14
will cause the low-to-high and high-to-low skews to become tighter over process, temperature and supply voltage extremes.
The output voltage bias generator
10
is problematic however, in that it can get into a condition (variation in process, temperature, supply voltage and resistor tolerance) where the biasp
12
and biasn
14
voltage levels supplied to the skew adjusting devices
102
,
104
in the output circuit
100
are at a “choking off” voltage level (i.e. weakening the skew devices
102
,
104
by supplying biasp
12
and biasn
14
voltage levels to their respective gates that are too close the operating voltage thresholds). Although a designer can adjust certain parameters associated with the output voltage bias generator
10
to compensate for specific conditions, such adjustments will degrade the skew adjusting capabilities of the output voltage bias generator
10
, and therefore reduce the usefulness of the output voltage bias generator
10
.
FIG. 2
is a waveform plot diagram
200
illustrating input and output waveforms
202
,
204
associated with the output voltage bias generator
10
and the output circuit
100
with a supply voltage of 3.3 volts at a nominal operating temperature of 25° C. Two operating conditions can be seen to need assistance. The first such operating condition is associated with a strong process coupled with a nominal resistance variation. The second such operating condition is associated with a strong process and a weak resistance variation. It can be appreciated that similar assistance is also necessary for other variations associated with process, temperature, supply voltage and resistor tolerance.
In view of the foregoing, a need exists for a bias generator and associated output circuit architecture that protects output skew voltage capabilities for the associated output circuit to a greater extent than that achievable using presently known circuit architectures.
SUMMARY OF THE INVENTION
The present invention is directed to a method as well as a bias generator and associated output circuit architecture that protects output skew voltage capabilities for the associated output circuit to a greater extent than that achievable using presently known circuit architectures. A differential-pair circuit detects bias voltage levels provided by the bias generator and provides a signal to skew adjusting assist devices within the associated output circuit when the bias voltage levels get close to a “choking off” voltage level. The signal turns on the skew adjusting assist devices to assist the skew adjusting devices.
According to one aspect of the invention, an improved output skew voltage bias generator is provided to enhance an existing circuit in achieving its skew adjusting potential without concern for the existing circuit defaulting to a condition with very slow propagation delay results.
According to another aspect of the invention, an improved output skew voltage bias generator is provided to enhance existing circuit manufacturing yields.
According to yet another aspect of the invention, an improved output skew voltage bias generator is provided to enhance an existing circuit in maximizing its skew adjusting potential such that the existing circuit will have smaller skew variations.
One embodiment of the present invention comprises a voltage bias generator comprising:
an output circuit having a plurality of voltage skew adjusting devices and a plurality of voltage skew assist devices, the output circuit responsive to an input signal to generate an output signal having a desired skew;
a bias voltage circuit configured to generate desired bias voltage signals for the plurality of voltage skew adjusting devices; and
a voltage sensing circuit responsive to at least one of the desired bias voltage signals to generate desired bias voltage signals for the plurality of voltage skew assist devices such that the output signal will have the desired skew.
Another embodiment of the present invention comprises a voltage bias generator comprising:
voltage skew adjusting means for adjusting an output skew voltage associated with an output signal in response to an input signal;
voltage skew assisting means for assisting the voltage skew adjusting means such that the voltage skew adjusting means will not be choked off during at least one marginal operating condition selected from the group consisting of temperature, process, supply voltage and resistor tolerance;
biasing means for biasing the voltage skew adjusting means; and
voltage detecting means for detecting bias voltage output signals associated with the biasing means and for generating desired bias voltage signals for the voltage skew assisting means such that the output signal will have a desired skew.
Yet another embodiment of the present invention comprises a voltage bias generator operational to sense an input voltage signal and generate an output signal having a desired voltage skew, the voltage bias generator comprising skew adjusting devices responsive to first internally generated bias signals and further comprisin
Brady W. James
Kempler William B.
Le Dinh T.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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