Electricity: power supply or regulation systems – Self-regulating – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-04-14
2001-04-03
Han, Jessica (Department: 2838)
Electricity: power supply or regulation systems
Self-regulating
Using a three or more terminal semiconductive device as the...
C323S314000, C323S907000
Reexamination Certificate
active
06211661
ABSTRACT:
BACKGROUND
1. Field of the Invention
This invention relates generally to integrated circuits and, more particularly, to a tunable constant current source with temperature and power supply compensation.
2. Discussion of the Related Art
The generation of a constant current or constant voltage is one of the most critical portions of any analog integrated circuit. Upon generating the constant current or constant voltage source, all other analog circuits are biased off this constant source within the integrated circuit itself. Historically, a constant current source has been supplied by use of a band-gap reference network that is formed by a diode and resistor to generate a constant current source.
While a band-gap reference network works well at conventional supply voltages, such as 5 volts (VCC), as power supply voltages decrease, the band-gap implementation becomes ineffective to inoperative. This is due to the diode drop which is between about 0.7 to 0.8 volts which does not scale and leaves less headroom for current source cascading. In most instances, a band-gap reference network will work well down to a supply voltage of about 2.5 volts and will operate with significant jitter down to about 1.8 volts. However, with new lower voltage power supplies operating in a range of about 1.5 volts, the band-gap reference network is not a viable option. Additionally, the band-gap reference network has undesirable power supply tracking characteristics. These characteristics cause excessive error with respect to power supply noise (delta in output due to delta in power supply).
Since constant current sources are generally used for phase lock loops (PLL) which are generally used to generate clocks for microprocessors, the above disadvantages have drastic effects on microprocessor operation. Moreover, since about 95% of all microprocessors use phase lock loops for generating clock pulses, this effects a broad range of microprocessors operating today. Thus, low power supply microprocessors may not use band-gap reference networks to provide constant current sources. In addition, because of the high sensitivity by band-gap reference networks to power supply changes, this creates jitter in the phase lock loop which adds directly to the cycle time of the processor, thereby reducing the operating speed and efficiency of the microprocessor.
What is needed then is a tunable constant current source with temperature and power supply compensation that does not suffer from the above-mentioned disadvantages. This will, in turn, provide a current source that has a very low sensitivity to power supply changes, provide a low clock skew and jitter in a phase lock loop, thereby reducing cycle time so that the microprocessor may run faster, provide operating supply voltage ranges between about 0.5 volts to about 1.8 volts, provide a constant current within an integrated circuit that can be used for any analog application, such as a phase lock loop which is used for processor clock generation, and provide a constant current source that compensates for temperature variations efficiently. It is, therefore, an object of the present invention to provide such a tunable constant current source with temperature and power supply compensation in an integrated circuit.
SUMMARY OF THE INVENTION
This invention is directed to a constant current source with temperature and power supply compensation which is formed within an integrated circuit. The tunable constant current source basically includes a voltage regulator, a differential amplifier, a current source and a compensating load which all operate to provide a tunable constant current source at low power supply voltage levels.
In one preferred embodiment, a tunable constant current source having temperature and power supply compensation includes a voltage regulator, a differential amplifier, a current source and a compensating load. The voltage regulator provides a substantially constant bias voltage V
B
. The different amplifier receives the bias voltage V
B
and maintains a load voltage V
L
substantially equal to the bias voltage V
B
by way of a negative feedback. The current source generates a substantially constant current IREF from the differential amplifier. The compensating load varies with temperature changes to maintain the current IREF substantially constant, whereby the tunable constant current source may operate in a supply voltage range between about 0.5 volts to about 1.8 volts.
In another preferred embodiment, a voltage regulator for use in a constant current source includes a negative feedback circuit, a gross temperature compensation circuit, a bias circuit and a temperature compensation circuit. The negative feedback circuit generates a substantially constant bias voltage V
B
. The gross temperature compensation circuit forms a portion of the negative feedback circuit and has a plurality of decodable branches with one of the plurality of branches selected to operate with the negative feedback circuit based upon an operating temperature of a circuit that employs the voltage regulator. The bias circuit operates to bias the negative feedback circuit with a reference voltage REFP. The temperature compensation circuit varies the reference voltage REFP during slight variations in the operating temperature of the circuit.
Use of the present invention provides a tunable constant current source with temperature and power supply compensation. As a result, the aforementioned disadvantages associated with the current band-gap reference network for use in providing a constant current source have been substantially reduced or eliminated.
REFERENCES:
patent: 4292583 (1981-09-01), Hoeft
patent: 4714872 (1987-12-01), Traa
Han Jessica
Harness & Dickey & Pierce P.L.C.
International Business Machines - Corporation
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