Amplifier protection circuit

• US 4,122,400 A
• Filed: 04/25/1977
• Issued: 10/24/1978
• Est. Priority Date: 11/08/1976
• Status: Expired due to Term

• Current Assignee: RCA Corporation
• Original Assignee: RCA Corporation
• Inventors: Schwabel, Paul Charles, Medendorp, Dale Frederick
• Primary Examiner(s): Mullins, James B.
• Application Number:
  US05/790,200
• Time in Patent Office: 547 Days
• Field of Search: 330/298, 330/207 P, 325/150, 325/151, 325/159
• US Class Current: 330/207.00P
• CPC Class Codes: H03F 1/52 Circuit arrangements for protecting such amplifiers monitoring arrangements G01R31/28; increasing reliability in communication systems, e.g. using redundancy H04B1/74
• CPC Class Codes: H03F 2200/204 A hybrid coupler being used at the output of an amplifier circuit
• CPC Class Codes: H03F 2200/468 the temperature being sensed
• CPC Class Codes: H03F 2200/504 the supply voltage or current being continuously controlled by a controlling signal, e.g. the controlling signal of a transistor implemented as variable resistor in a supply path for, an IC-block showed amplifier
• 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: H04B 1/0466 Fault detection or indication H04B1/0483 takes precedence
• CPC Class Codes: H04B 17/103 Reflected power, e.g. return loss
• CPC Class Codes: H04B 17/18 Monitoring during normal operation

Abstract

A protection circuit for a transmitter amplifier is provided in which separate VSWR (reflected power) control and separate temperature control is provided when the thresholds of either or both are exceeded. When the temperature of the RF amplifier is sensed and when this temperature exceeds a certain threshold level, the output level of the RF amplifier is adjusted to protect the amplifier. Separately, there is provided a means for sensing the ratio of the reflected power to the forward power and when this ratio exceeds a given threshold, the gain of the amplifier is cut back to thereby protect.

Claims

1. The protection circuit for controlling the power of a transmitter amplifier which produces an output varying with a control signal applied thereto comprising:

first sensing means coupled to said transmitter amplifier for sensing the forward power provided therefrom,

second sensing means coupled to said transmitter amplifier for sensing the reflected power thereto, and

means coupled to said first and second sensing means for providing a control signal which varies in relation to only said forward power below a fixed predetermined threshold ratio of reflected power to forward power and which varies in relation to reflected power above said fixed predetermined threshold ratio regardless of temperature change unless the temperature at said amplifier exceeds a predetermined threshold considered alone to be an unsafe heat condition of said amplifier, whereby the power output from the transmitter amplifier is maximized until the ratio of reflected power to forward power exceeds said given threshold ratio.

2. The combination of claim 1 wherein said means for providing a control signal includes temperature sensing means responsive to only the temperature of said transmitter amplifier for providing a control signal to said transmitter amplifier to lower the output therefrom when only said sensed temperature exceeds said predetermined threshold considered to be an unsafe heat condition of said amplifier.

3. The combination claimed in claim 1, wherein said means for providing a control signal includes first and second peak detectors with said first peak detector coupled to said first sensing means and said second peak detector coupled to said second sensing means and said second peak detector including a diode being reverse biased by the peak detected level from said first peak detector until the value of the detected reflected power exceeds the reverse bias level established by the forward power.

4. The combination claimed in claim 3, including a comparator having one terminal thereof coupled to a source of reference voltage and a comparison terminal coupled to said peak detectors.

5. A protection circuit for a transmitter amplifier which produces an output which varies with a control signal applied thereto, comprising:

sensing means being responsive to the forward power at the output of said transmitter amplifier for providing a forward power signal which varies in relation to said forward power,

reflected power sensing means coupled to the output of said transmitter amplifier to develop a reflected power signal which varies in proportion to the reflected power,

means coupled to said forward and reflected power sensing means to develop a first signal which varies in relation to only said forward power below a fixed predetermined threshold ratio of reflected power to forward power and which varies in relation to reflected power above said fixed predetermined threshold ratio regardless of temperature change,

means for providing a reference signal,

signal comparing means responsive to said first signal and said reference signal for developing a control signal which varies in accordance with the difference between said reference signal and said first signal,

means coupling said signal comparing means to the transmitter amplifier and applying said control signal thereto to control the power output from said transmitter amplifier, and

temperature sensing means sensing the temperature of said transmitter amplifier and having a characteristic in accordance with said temperature, said reference signal being responsive to said temperature sensing means variations above a predetermined temperature level that is considered to be an unsafe heat condition of said amplifier to vary said reference signal whereby the difference between said first signal and reference signal changes.