Automatic level control circuit for dual mode analog/digital cellular telephone

• US 5,438,683 A
• Filed: 09/19/1994
• Issued: 08/01/1995
• Est. Priority Date: 03/02/1992
• Status: Expired due to Term

• Current Assignee: Novatel Wireless Solutions (Inseego Corp.)
• Original Assignee: Novatel Communications Incorporated
• Inventors: Durtler, Willem G., Anvari, Kiomars, Tsien, Chih C.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): Charouel, Lisa
• Application Number:
  US08/308,636
• Time in Patent Office: 316 Days
• Field of Search: 455/74, 455/89, 455/116, 455/126, 455/127, 455/93, 455/102, 455/249.1, 455/115, 375/5, 375/98, 330/284, 330/129, 330/141, 330/280, 330/281, 370/11, 379/58, 379/59
• US Class Current: 455/74
• CPC Class Codes: H03G 3/3047 for intermittent signals, e.g. burst signals

Abstract

An automatic level control circuit for cellular telephone transmitters which is compatible with both existing analog cellular service and expected next generation digital TDMA service. The circuit automatically and dynamically changes modes to maintain communication when a mobile subscriber moves from one type of service to another. In a first mode of operation, which is compatible with existing analog cellular service, the circuit provides a closed loop negative feedback circuit which produces a control signal for continuously controlling the output power level of the transmitter amplifier. In a second mode of operation, which is compatible with proposed digital TDMA service, the circuit operates to alternately close the negative feedback loop during the periods when the transmitter is permitted to transmit (assigned TDMA frames) and open the loop during other periods when the transmitter is turned off. When the loop is opened, the invention temporarily stores the magnitude of the control signal. This stored value is subsequently used to quickly restore the amplifier to its assigned power level during successive frames when the loop is again closed for burst transmission.

Claims

1. In a cellular telephone transceiver, a radio frequency amplifier for amplifying either an analog input signal or a digital input signal, said radio frequency amplifier comprising:

a variable attenuator, responsive to a power control signal, for receiving and attenuating digital associated signals associated with the digital input signal to produce an attenuated signal and passing the attenuated signal to a controllable-gain amplifier during a first mode of operation, said controllable-gain amplifier amplifying said attenuated signal to produce an amplifier output signal associated with said digital input signal;

switching means for allowing analog associated signals associated with the analog input signal to bypass said variable attenuator and for applying said power control signal to said controllable-gain amplifier during a second mode of operation said controllable-gain amplifier producing an amplifier output signal associated with said analog input signal;

a detector connected to receive the amplifier output signal produced by said controllable-gain amplifier and responsively produce a detected signal indicative of the power level of the amplifier output signal;

means for comparing the detected signal to a preselected reference signal and responsively producing said power control signal such that said power control signal is indicative of a difference between said detected signal and said reference signal;

control means, responsive to an operating mode signal, for alternately storing the power control signal and applying the power control signal to the variable attenuator during the first mode of operation; and

means for producing said operating mode signal.

2. The radio frequency amplifier of claim 1 further comprising a step attenuator for receiving and attenuating either of said analog or digital input signals to produce, respectively, the analog associated signal or the digital associated signal and passing that signal to the switching means, said step attenuator responsive to one or more power level signals which represent a preselected power level for said amplifier output signal.

3. The radio frequency amplifier of claim 1 further comprising means for sampling and attenuating the amplifier output signal by one of a plurality of predetermined values and passing the attenuated amplifier output signal to the detector, whereby variation in the magnitude of the attenuated amplifier output signal is substantially reduced as compared to variation in the magnitude of the amplifier output signal.

4. The radio frequency amplifier of claim 3 wherein the detector comprises a diode and the variation in the magnitude of the attenuated amplifier output signal is sufficiently reduced such that said diode does not require temperature compensation.

5. The radio frequency amplifier of claim 3 wherein the sampling and attenuating means comprises a plurality of impedances connected to a switch, and said switch receives the amplifier output signal and, via one of said impedances, attenuates the amplifier output signal to produce said attenuated amplifier output signal and applies said attenuated amplifier output signal to said detector.

6. The radio frequency amplifier of claim 1 wherein said means for comparing includes a low pass filter for removing higher frequency components from the detected signal to produce a filtered detected signal, a summing amplifier for producing an error signal which is indicative of a difference in magnitude between the filtered detected signal and the preselected reference signal, an integrator for integrating the error signal to produce an integrated error signal, and a level adjuster for adjusting the magnitude of the integrated error signal to produce the power control signal.

7. The radio frequency amplifier of claim 1 wherein the operating mode signal has first and second logical levels for defining said first and second modes of operation, respectively.

8. The radio frequency amplifier of claim 1 wherein during the first operating mode said controllable-gain amplifier amplifies said digital associated signal and said power control signal is alternately applied to said controllable-gain amplifier during predetermined periods when said transceiver is transmitting and stored during periods when said transceiver is not transmitting.

9. The radio frequency amplifier of claim 1 wherein the control means includes a capacitor which is charged by said power control signal.

10. In a cellular telephone transceiver, a method for controlling a power level of an output signal produced by an amplifier, said amplifier being capable of producing the amplifier output signal associated with either an analog input signal during an analog mode of operation or a digital input signal during a digital mode of operation, said method comprising the steps of:

A. determining whether to use the analog mode of operation or the digital mode of operation;

B. detecting the amplifier output signal and responsively producing a detected signal which is indicative of the power level of the output signal;

C. comparing the detected signal to a preselected reference signal and responsively producing a power control signal which is indicative of a difference between said detected signal and said reference signal;

D. during the analog mode of operation, forgoing attenuation and applying to the amplifier an associated analog signal that is associated with the analog input signal, and using the power control signal to continuously adjust the power level of the amplifier output signal produced by the amplifier in response to the associated analog signal;

E. during the digital mode of operation, alternately storing the power control signal and using the power control signal to adjust a variable attenuator, the variable attenuator receiving an associated digital signal that is associated with the digital input signal and attenuating the associated digital input signal to produce an attenuated input signal, said variable attenuator passing the attenuated input signal to the amplifier.

11. The method of claim 10 further including the step of applying either the analog input signal or the digital input signal to a step attenuator, said step attenuator producing respectively the associated analog signal or the associated digital signal associated with the applied analog or digital input signal, and using this signal in step D if operating in the analog mode or step E if operating in the digital mode.