Timing control circuit

Details Timing control circuit Timing control circuit

2002-04-12

2004-02-03

Callahan, Timothy P. (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Signal converting, shaping, or generating

Synchronizing

C327S142000, C327S198000

Reexamination Certificate

active

06686781

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates generally to timing control circuits and in particular to a timing control circuit providing a wide dynamic range. Timing circuits are used in a number of applications such as pulse width modulation (PWM), voltage controlled oscillators (VCO), etc.
FIG. 1
is a schematic diagram of an existing timing circuit
10
used in a PWM application. As known in the art, a PWM signal is a series of pulses. A controllable current source
12
is used to charge a capacitor
14
. When the capacitor
14
reaches a certain voltage, established by a reference voltage applied to the inverting terminal of operational amplifier
16
, operational amplifier
16
changes states causing a pulse to end.
A drawback to the circuit of
FIG. 1
is that it is difficult to provide a large dynamic range. For a given value of capacitor
14
, a very large current is needed to generate narrow pulse widths (i.e., rapid charging of capacitor
14
). On the other hand, very small current is needed to provide wide pulse widths (i.e., slow charging of capacitor
14
). Unfortunately, controlling small currents can be difficult leading to unstable, wide pulse widths.
If capacitor
14
is increased in value to allow larger currents to be used for larger pulse widths, this creates a detriment in generating narrow pulse widths. If capacitance of capacitor
14
is increased, then larger currents are need to generate small pulse widths. Thus, it is difficult to provide a wide dynamic range pulse widths with the existing timing circuit.
BRIEF SUMMARY OF THE INVENTION
An exemplary embodiment of the invention is a timing circuit comprising a controllable current source and a capacitor coupled to the current source. A resistor and a second capacitor are connected in series. The series resistor and second capacitor are connected in parallel with the capacitor. A trigger circuit has a first terminal coupled to the capacitor. The trigger circuit changes states when a voltage at the first terminal exceeds a reference voltage.


REFERENCES:
patent: 4413313 (1983-11-01), Robinson
patent: 4463317 (1984-07-01), Kusakabe
patent: 5729443 (1998-03-01), Pavlin
National Semiconductor, 1995 Power IC Databook, pp. 3-3 and 3-39.
Texas Instruments, TPS67341, Fixed 12-V 120-mA Boost-Converter Supply, p. 4-148, Aug. 1995.
National Semiconductor, Application Note 115, Wide Range Function Generator, pp. 369-371, date unknown.
National Semiconductor, Application Note 30, Log Converters, pp. 76-79, date unknown.
National Semiconductor, Application Note 240, Robert A. Pease, Wide-Range Current-to-Frequency Converters, pp. 574-579, date unknown.
HFPC, Apr. 1994 Proceedings, pp. 154, 165, 166, 167.

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