Oscillators – Ring oscillators
Reexamination Certificate
1999-05-25
2001-12-04
Grimm, Siegfried H. (Department: 2817)
Oscillators
Ring oscillators
C331S034000, C331S175000, C331S176000, C331S17700V, C327S103000
Reexamination Certificate
active
06326855
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates generally to voltage-controlled oscillators (VCOs), and more particularly to converting a voltage to a current for use in a current-controlled oscillator (ICO) in which process, voltage, and temperature variations can be compensated independently.
2. Discussion of Background Art
Voltage controlled oscillators using Complementary Metal-Oxide Semiconductor (CMOS) technologies are known to be greatly affected by process, voltage supply, and temperature variations. U.S. Pat. No. 5,061,907 to Rasmussen and U.S. Pat. No. 5,331,295 to Jelinek et al. are directed to achieving automatic compensation for process, voltage, and temperature effects.
Rasmussen discloses a VCO that includes a multistage ring oscillator, a voltage-to-current converter, process compensation circuitry, and a trip-point compensation circuit. The voltage-to-current converter linearly converts an input signal to an output current signal that is independent of varying process and temperature effects on the transistor in the ring oscillator. The converter thus provides a variable control current. The process compensation circuitry responds to the tuning voltage input signal to provide a current dump output signal. However, this signal is dependent on the transistor strength, which in turn depends on the transistor fabrication process, supply voltage, and operating temperature. The trip-point compensation circuit subtracts the process compensation current from the voltage-to-current converter generated current to produce a net current.
Jelinek et al. discloses a VCO including a multistage ring oscillator, a first current source, a second current source, and an attenuator. The first current source provides a substantially constant current independent of process, supply voltage, and temperature. The second current source provides a current that varies in response to process, supply voltage, and temperature. Both current sources generate respective current signals independent of the input signal to the VCO. The attenuator, responsive to the VCO's input voltage signal, provides to the ring oscillator a control current signal which determines the frequency of oscillation of the ring oscillator.
Neither Rasmussen nor Jelinek et al. can control or regulate the quantity of process, voltage supply, and temperature compensation, or adjust each of these variables independently. Such ability is a common need in VCO designs.
SUMMARY OF THE INVENTION
The present invention provides a voltage-to-current (V-to-I) converter that can meet the process, voltage, and temperature-varying current needs of a current-controlled oscillator (ICO). It also provides a circuit designer the ability to independently adjust the amount of compensation for process, voltage, and temperature variations, and thereby minimize their effect on a VCO. Additionally, the ICO or a VCO utilizing the invention is better stabilized.
The V-to-I converter circuit receives an input voltage V
in
and, based on the voltage range of operation of V
in
, converts V
in
to at least one output current I
out
, which ranges itself according to the process, supply voltage, and temperature needs of the ICO. The V-to-I converter circuit includes an uncompensated current source, a compensated current generator, and a modulator. The uncompensated current source provides a current that is proportional to the strength of the p-channel transistors and is used to reduce the process effect on an associated ICO circuit. The compensated current generator includes adjustable and distinct components to compensate for each of process, supply voltage, and temperature effects. Thus, the compensated current generator generates a current that reflects the process, supply voltage, and temperature needs of the ICO over variations in process, supply voltage, and temperature. The modulator by itself is a process, supply voltage, and temperature stable circuit which receives the same voltage V
in
operating in a range and generates a current which ranges itself in response to the current needs of the ICO.
Less current I
out
from the V-to-I converter is provided when process, temperature, and voltage effects are strong, and more current I
out
is provided when process, temperature, and voltage effects are weak.
In another embodiment of the invention, the V-to-I converter includes circuits for process and temperature compensation only. Voltage compensation is optional since the voltage supply for the V-to-I converter circuit runs off a linearly regulated voltage supply in the same chip.
Current I
out
may be replicated to produce two or more similar currents to control two or more similar ICO circuits, separately or simultaneously. Similarly, the uncompensated current source's output current may be replicated to produce two or more similar output currents each independently feeding two or more similar compensated current generator circuits. The resulting circuit is therefore able to utilize one or more I
out
from different circuit configurations. In one example, only one of these compensated current generator circuits may be active for a given time period while sharing the modulator circuitry. In another example, each compensated current generator circuit may be connected to a corresponding separate instance of the modulator circuitry which in turn drives one or more separate and corresponding ICO circuits.
REFERENCES:
patent: 5061907 (1991-10-01), Rasmussen
patent: 5331295 (1994-07-01), Jelinek et al.
patent: 5847616 (1998-12-01), Ng et al.
patent: 6011822 (2000-01-01), Dreyer
Brown Michael Arthur
Jelinek Jules Joseph
Shirani Ramin
Agere Systems INC
Grimm Siegfried H.
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