Amplifier protection circuit

Claim 2

A protection circuit for controlling the power of a transmitter amplifier which produces an output varying with a control signal applied thereto, said circuit including in combination: first circuit means coupled to the transmitter amplifier output for sensing the forward power coupled therefrom, said first circuit means developing a first signal which varies in accordance with the sensed forward power; bias circuit means for developing a second signal; signal comparing means coupled to said first circuit means and said bias circuit means for comparing said first and second signals, said signal comparing means developing a control signal which varies in accordance with the difference between said first and second signals, said signal comparing means being coupled to the transmitter amplifier for applying said control signals thereto to vary the power developed by the transmitter amplifier; and delayed power level sensing circuit means coupled to said first circuit means and said bias circuit means, said delayed circuit means being operative in response to said forward power being below a predetermined level for a predetermined period of time to reduce said second signal, said comparison means being operative in response to said redUced second signal to reduce said control signal for decreasing said transmitter amplifier power.

Claim 3

The protection circuit of claim 1 wherein said transmitter amplifier includes an amplifier stage having a power output which varies in accordance with said control signal, and further including limit circuit means coupled to said amplifier stage and said comparison means and responsive to said control signal exceeding a predetermined level to increase said first signal, said comparison means operative in response to said increased first signal to reduce said control signal whereby said control signal is maintained below a preset level.

Claim 4

The protection circuit of claim 2 wherein said delayed power level sensing circuit means includes time delay means coupled to said first circuit means and responsive to said forward power being below said predetermined level for said predetermined period of time to develop a delayed signal, and semiconductor means coupled to said time delay means and responsive to said delayed signal exceeding a second predetermined level to reduce said second reference signal.

Claim 5

The protection circuit of claim 3 wherein said time delay means is an integrator and said semiconductor means is a programmable unijunction transistor.

Claim 6

The protection circuit of claim 4 wherein said limit circuit means includes diode means being coupled to said amplifier stage and said comparison means, said diode means operative in response to said control signal exceeding said predetermined level to conduct and couple a control voltage to said comparison means for increasing said first signal.

Claim 7

A protection circuit for a transmitter amplifier which includes an amplifier stage having a power output which varies with a control signal applied thereto and operating when a supply voltage is applied thereto, said circuit including in combination: sensing means coupled to the output of the transmitter amplifier, said sensing means being responsive to forward power coupled therefrom to develop a forward power signal which varies in relation to said forward power, said sensing means further being responsive to reflected power coupled to the transmitter amplifier to develop a reflected power signal which varies in relation to said reflected power; first circuit means coupled to said sensing means and responsive to said forward power signal to develop a first signal which varies in relation to said forward power; bias circuit means for developing a reference signal; signal comparing means coupled to said first circuit means and to said bias circuit means, said signal comparing means being responsive to said reference signal and to said first signal to develop 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 stage and applying said control signal thereto to control the power developed by said transmitter amplifier stage; temperature sensing means coupled to said bias means, said temperature sensing means sensing the temperature of said transmitter amplifier and having a characteristic varying in accordance with said temperature, said bias means being responsive to said temperature sensing means variations to vary said reference signal whereby the difference between said first signal and said reference signal changes; second circuit means coupled to said sensing means, said second circuit means being responsive to said reflected power signal to develop a second signal which varies in relation to said reflected power, said second circuit means being coupled to said bias circuit means, said bias circuit means being responsive to said second signal which reaches a predetermined value to vary said reference signal whereby the difference between said first signal and said reference signal changes; delayed power level sensing circuit means coupled to said first circuit means and to said bias circuit means, said delayed circuit means being opErative in response to said forward power being below a predetermined level for a predetermined period of time to reduce said reference signal whereby the difference between said first signal and said reference signal is reduced; and limit circuit means coupled to said transmitter amplifier stage and said first circuit means and responsive to said control signal exceeding a predetermined level to increase said first signal whereby the difference between said first signal and said reference signal is decreased, said comparison means being operative in response to said decreased difference between said first signal and said reference signal to reduce said control signal for decreasing said transmitter amplifier stage power.

Claim 8

A protection circuit for a transmitter amplifier which includes an amplifier stage having a power output which varies with a control signal applied thereto and operating when a supply voltage is applied thereto, said circuit including in combination: sensing means coupled to the output of the transmitter amplifier, said sensing means being responsive to forward power coupled therefrom to develop a forward power signal which varies in relation to said forward power, said sensing means further being responsive to reflected power coupled to the transmitter amplifier to develop a reflected power signal which varies in relation to said reflected power; first circuit means coupled to said sensing means and responsive to said forward power signal to develop a first signal which varies in relation to said forward power; bias circuit means for developing a reference signal; signal comparing means coupled to said first circuit means and to said bias circuit means, said signal comparing means being responsive to said reference signal and to said first signal to develop 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 stage and applying said control signal thereto to control the power developed by said transmitter amplifier stage; temperature sensing means coupled to said bias means, said temperature sensing means sensing the temperature of said transmitter amplifier and having a characteristic varying in accordance with said temperature, said bias means being responsive to said temperature sensing means variations to vary said reference signal whereby the difference between said first signal and said reference signal changes; second circuit means coupled to said sensing means, said second circuit means being responsive to said reflected power signal to develop a second signal which varies in relation to said reflected power, said second circuit means being coupled to said bias circuit means, said bias circuit means being responsive to said second signal which reaches a predetermined value to vary said reference signal whereby the difference between said first signal and said reference signal changes; delayed power level sensing circuit means coupled to said first circuit means and to said bias circuit means, said delayed circuit means being opErative in response to said forward power being below a predetermined level for a predetermined period of time to reduce said reference signal whereby the difference between said first signal and said reference signal is reduced; and limit circuit means coupled to said transmitter amplifier stage and said first circuit means and responsive to said control signal exceeding a predetermined level to increase said first signal whereby the difference between said first signal and said reference signal is decreased, said comparison means being operative in response to said decreased difference between said first signal and said reference signal to reduce said control signal for decreasing said transmitter amplifier stage power.