Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Unwanted signal suppression
Reexamination Certificate
1999-11-17
2001-10-16
Lam, Tuan T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Unwanted signal suppression
C327S552000, C327S554000
Reexamination Certificate
active
06304135
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to the field of electronic amplifier circuits, and more particularly to a tuning method and circuit for a G
m
/C filter circuit.
BACKGROUND OF THE INVENTION
The recent trend towards the miniaturization of electronic circuits is driven by consumer demand for smaller and light-weight electronic devices such as cellular phones and portable computers. Often, the heaviest component in an electronic device is the battery. Smaller batteries are able to provide less power. As batteries become smaller, integrated circuits (ICs) need lower working voltages and power consumption to prevent the battery from discharging too rapidly. As appliances and circuit designs continue to decrease in size and increase in speed, the need for low power, low noise, current efficient filter circuits increases.
One configuration for a continuous time filter having a transconductor needs tuning to accommodate for resistive/capacitive (RC) effects and components of the circuitry. Transconductance (G
m
) is defined as the proportionality constant that is a function of the output signal current component and the instantaneous input voltage of the transconductor.
SUMMARY OF THE INVENTION
The present invention achieves technical advantages as a tuning method and circuit for G
m
/C filters. The circuit and method is useful in a variety of applications, particularly in amplifier circuits for small portable electronic devices such as cellular phones and laptop computers.
In one embodiment, disclosed is a method of tuning a G
m
/C filter having a transconductive G
m
stage and an output capacitor, the G
m
/C filter having a first circuit portion including a variable current source. The method includes the step of calibrating the output capacitor iteratively with the variable current source to tune the G
m
/C filter.
In another embodiment, disclosed is a method of tuning a G
m
/C filter having a transconductance G
m
stage and an output capacitor, including the step of establishing a bias current with an external precision resistor, where the transconductance G
m
of the G
m
/C filter is a function of the external precision resistor. The bias current is scaled with a scaling factor adapted to calibrate the G
m
/C circuit output capacitor.
Also disclosed is a G
m
/C filter and tuning circuit therefore having a transconductance and a capacitor, including a first circuit portion adapted to couple to the filter and iteratively tune the capacitance of the filter capacitor.
The present invention is advantageous in providing a tuning circuit and method that shuts off once the G
m
and C
INT
components are calibrated, requiring no operational current, saving power and thereby increasing battery life. This is advantageous over prior art PLL-type tuning circuits that require continuous current. Also, the circuits of the present invention require very little semiconductor area, compared to other tuning schemes which require large cells. Very little additional circuitry is required with most of the circuits already existing in a typical G
m
/C filter. A circuit including an op amp, a variable current source block, and an algorithm in the digital circuitry are the only additional components of the present invention. Furthermore, the on-chip algorithm and circuit for tuning a G
m
/C filter described has no detrimental dynamic effects on the filter circuitry, and tuning is completed in fewer clock cycles than in prior art circuits.
REFERENCES:
patent: 5606277 (1997-02-01), Feliz
Brady W. James
Lam Tuan T.
Mosby April M.
Nguyen Hiep
Telecky , Jr. Frederick J.
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