Linear power control loop

• US 6,417,729 B1
• Filed: 01/26/2000
• Issued: 07/09/2002
• Est. Priority Date: 02/18/1999
• Status: Expired due to Fees

• Current Assignee: Itron, Inc.
• Original Assignee: Itron, Inc.
• Inventors: Brunn, Brian T., Lofstad, Eric W., Lemay, Normand T., MacConnell, John W., Sadowski, Eric
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): NGUYEN, KHANH V
• Application Number:
  US09/491,538
• Time in Patent Office: 895 Days
• Field of Search: 330/129, 414/0, 428/5, 435/0, 327/346
• US Class Current: 330/129
• CPC Class Codes: G01R 21/10 by using square-law characteristics of circuit elements, e.g. diodes, to measure power absorbed by loads of known impedance G01R21/02 takes precedence
• CPC Class Codes: G01R 21/14 Compensating for temperature change
• CPC Class Codes: H03B 5/04 Modifications of generator to compensate for variations in physical values, e.g. power supply, load, temperature
• CPC Class Codes: H03C 1/06 Modifications of modulator to reduce distortion, e.g. by feedback, and clearly applicable to more than one type of modulator
• CPC Class Codes: H03F 1/345 using hybrid or directional couplers
• CPC Class Codes: H03F 3/45475 using IC blocks as the active amplifying circuit
• CPC Class Codes: H03G 3/004 Control by varying the supply voltage
• CPC Class Codes: H03G 3/3042 in modulators, frequency-changers, transmitters or power amplifiers transmission power control in bidirectional transmission systems H04W52/04
• CPC Class Codes: H03L 1/02 against variations of temperature only
• CPC Class Codes: H03L 7/18 using a frequency divider or counter in the loop H03L7/20, H03L7/22 take precedence
• CPC Class Codes: Y10S 323/907 Temperature compensation of semiconductor

Abstract

The present invention presents a closed loop system that utilizes a non-linear reference to control a power amplifier'"'"'s output power in order to obtain a linear transfer function of dB per adjustment step of a reference input. The closed loop system demonstrates that each non-linear stage/step in an automatic gain control system can create a linear closed loop system when using a non-linear reference. The closed loop system of the present invention eliminates the need for a linearization circuit for the system'"'"'s power detector. The closed loop system may be used with most power amplifiers when linear control in terms of dB vs. adjustment setting of the input reference signal is desired. Output power in terms of dBms can be accurately set in linear steps where power control over a wide dynamic range is desired.

Claims

1. A closed power control loop that produces a linear transfer function in response to an adjustable non-linear reference input, comprising:

an adjustable power amplifier, wherein said adjustable power amplifier includes a power input, a control input and a power output;

a power detector, wherein said power detector detects said power output of said adjustable power amplifier and produces a power detector output;

an adjustable, non-linear reference signal; and

a comparator wherein said comparator compares said power detector output with said reference signal and produces a comparator output representative of the difference between said power detector output and said reference signal,

wherein said comparator output is provided to said power amplifier in the form of said control input and said power amplifier adjusts said power input with said control input to produce a non-linear power output variation, wherein said non-linear power output variation is substantially linear with respect to an adjustment in said non-linear reference signal said adjustable non-linear reference signal being provided by a programmable potentiometer (EEPOT).

2. The closed power control loop of claim 1, wherein said power detector output is a non-linear signal.

3. The closed power control loop of claim 1, wherein said adjustable, non-linear reference signal is adjusted exponentially.

4. The closed power control loop of claim 3, wherein the exponential adjustment is performed through a plurality of linear steps.

5. The closed power control loop of claim 1, further comprising a loop filter wherein said loop filter sets a control loop bandwidth.

6. The closed power control loop of claim 1, wherein said control input is non-linear.

7. The closed power control loop of claim 1, wherein said non-linear output power variation is exponential.

8. A closed power control loop that produces a linear transfer function in response to an adjustable non-linear reference input, comprising:

power amplifying means for receiving and amplifying a power input, for receiving a control input, and for producing a power output, wherein amplifying said power input is performed in response to the received control input to produce a non-linear variation of said power output;

power detection means for detecting said power output of said power amplifying means and for producing a power detection means output;

adjustable input means for providing an adjustable non-linear reference output; and

comparison means for comparing said power detection means output with said reference output and for providing a comparison means output representative of the difference between said power detection means output and said reference output,

wherein said comparison means output is provided to said power amplifying means in the form of said control input and wherein said non-linear variation of said power output is substantially linear with respect to an adjustment in said non-linear reference output said adjustable input means being a programmable potentiometer (EEPOT).

9. The closed power control loop of claim 8, wherein said power detection means output is non-linear.

10. The closed power control loop of claim 8, wherein said adjustable non-linear reference output is adjusted exponentially.

11. The closed power control loop of claim 10, wherein the exponential adjustment is performed through a plurality of linear steps.

12. The closed power control loop of claim 8, further comprising filter means for setting a closed loop bandwidth.

13. The closed power control loop of claim 8, wherein said control input is non-linear.

14. The closed power control loop of claim 8, wherein said non-linear variation of said power output is exponential.

15. A method for controlling a power amplifier to produce a substantially linear transfer function in response to an adjustable non-linear reference input, comprising the steps of:

providing a power input to said power amplifier;

producing a power output from said power amplifier;

detecting said power output;

providing an adjustable, non-linear reference signal;

comparing said reference signal with the detected power output;

producing a comparison output representative of the difference between said reference signal and said detected power output;

providing said comparison output to said power amplifier in the form of a control input; and

amplifying said power input with said power amplifier in response to said control input to produce a non-linear variation in said power output,

adjusting said adjustable non-linear reference signal, wherein said non-linear power output variation is substantially linear with respect to the adjustment in said non-linear reference signal said adjustable non-linear reference signal being provided by a programmable potentiometer (E²POT).

16. The method of claim 15, wherein the step of adjusting comprises adjusting said adjustable non-linear reference signal exponentially.

17. The method of claim 16, wherein adjusting said adjustable non-linear reference signal exponentially is performed through a plurality of linear steps.