Automatic gain control arrangement useful in an FM radio receiver

Claim 2

In a receiver for processing RF signals modulated to represent information by time relationships, apparatus comprising: tuner means responsive to said RF signals for deriving an IF signal from a selected one of said RF signals; IF means including a plurality of cascaded limiter amplifier stages for successively amplifying said IF signal to form a pulse signal; information detector means for detecting the time relationship of said pulse signal to develop an information signal; auxiliary amplifier means beside said cascade of said limiter amplifier stages and including gain control means responsive to an auxiliary control signal for amplifying an intermediate signal developed at an intermediate point in said cascade to develop an output signal; detector means for generating an amplitude representative signal having a magnitude representing the amplitude of said output signal of said auxiliary amplifier means; control signal generating means for generating a main control signal and said auxiliary control signal in response to said amplitude representative signal, said control signal generating means includes non-linear processing means for causing the magnitude of said auxiliary control signal to be non-linearly related to the magnitude of said main control signal; and utilization means for controlling a predetermined function of said receiver in response to said main control signal.

Claim 3

The apparatus recited in claim 1 wherein: said non-linear signal means includes a logarithmic amplifier for generating said auxiliary control signal in response to said amplitude representative signal so that the amplitude of said auxiliary control signal has an amplitude which is a logarithmic function of the magnitude of the amplitude representative signal.

Claim 4

The apparatus recited in claim 2 wherein: said gain control means includes a differential amplifier having a differential input to which said auxiliary control signal is applied and a common input to which said intermediate signal is applied.

Claim 5

The apparatus recited in claim 3 wherein: said detector means includes first converter means for converting said amplitude representative signal to a corresponding amplitude representative current; and said logarithmic amplifier includes a bipolar transistor having base, emitter and collector electrodes; a resistor connected between said emitter and a point of reference potential; and a diode connected between said base and said point of reference potential, said amplitude representative current being applied to said diode; and second converter means for converting a current developed at the collector of said transistor to a voltage, said voltage being applied to said differential input of said differential amplifier.

Claim 6

The apparatus recited in claim 4 wherein: said second converter means includes a second resistor having a high resistance value compared to the resistance value of said first mentioned resistor.

Claim 7

The apparatus recited in claim 5 wherein: said auxiliary amplifier means is responsive to the output signal of the first one of said limit amplifier stages.

Claim 8

The apparatus recited in claim 6 wherein: said auxiliary amplifier means includes an amplifier stage, including a degenerative feedback path, coupled between said predetermined point and said gain control means.

Claim 9

The apparatus recited in claim 7 wherein: said detector means includes amplitude limiting means for inhibiting the amplitude of said amplitude representative signal from exceeding a predetermined level.

Claim 10

The apparatus recited in claim 8 wherein: said control means generates first and second main control signals having magnitudes which change in opposite senses in response to said amplitude representative signals.

Claim 11

The apparatus recited in claim 1 wherein: said utilization means comprises a gain control amplifier in said tuner means for reducing the amplitudes of said RF signals as the amplitude of said intermediate signal increases.

Claim 12

The apparatus recited in claim 1 wherein: said auxiliary amplifier means includes input means for developing an input current in response to said intermediate signal; and differential amplifier means for amplifying said input current to develop an output current including gain control means for controlling the gain of said differential amplifier means in response to a control voltage; said non-linear processing means includes logarithmic means for developing a logarithmic voltage having magnitude related to the logarithm of the amplitude of the output current of said differential amplifier; subtraction means for subtracting a substantially constant voltage from said logarithmic voltage to obtain a difference voltage; and multiplication means for multiplying said difference voltage by a constant greater than one to develop said control voltage.

Claim 13

The apparatus recited in claim 11 wherein: said logarithmic means includes a first transistor having base, emitter and collector electrodes, said base and collector electrodes of said first transistor being connected together, said collector electrode of said first transistor being coupled to be responsive to said output current, said emitter electrode of said first transistor being connected to a circuit point; said subtraction means includes a second transistor having base, emitter and collector electrodes, said base electrode of said second transistor being connected to the collector electrode of said first transistor; and a first resistor connected between said emitter electrode of said second transistor and said circuit point; and multiplication means includes a second resistor coupled to said collector electrode of said second transistor having a resistance value greater than the resistance value of said first resistor.

Claim 14

The apparatus recited in claim 12 wherein: said differential amplifier includes third and fourth transistors each having base, emitter and collector electrodes, said emitter electrodes of said third and fourth transistors being connected together, said input current being applied to said emitter electrodes of said third and fourth transistors, said output current being provided at one of said collectors of said third and fourth transistors, one of said bases of said third and fourth transistors being connected at a point between said collector of said second transistor and said second resistor.

Claim 15

The apparatus recited in claim 13 wherein: a current mirror amplifier is coupled between the collector of said second transistor and said second resistor.

Claim 16

The apparatus recited in claim 14 wherein: a peak detector including a filter capacitor is coupled between said one of said collectors of said third and fourth transistors and said collector of said first transistor.

Claim 17

Apparatus comprising: input means for supplying an angle-modulated carrier; limiter means including a plurality of cascaded limiter stages for successively amplifying said angle-modulated carrier for forming a pulse signal; information detector means for deriving an information signal in response to said pulse signal; first and second linear amplifier stages coupled in cascade beside at least a portion of said cascade of said limiter amplifier stages for amplifying an intermediate signal developed at an intermediate point in said cascade to develop an output signal, said first linear amplifier including a degenerative feedback path, said second linear amplifier including gain control means; detector means for generating an amplitude representative signal in response to said output signal having a magnitude representing the amplitude of said output signal; control means responsive to said amplitude representative signal for generating a main control signal having a magnitude substantially linearly related to the magnitude of said amplitude representative signal and an auxiliary control signal having a magnitude substantially non-linearly related to the magnitude of said amplitude representative signal; and utilization means for utilizing said main control signal; said auxiliary control signal being applied to said gain control means for degeneratively controlling the gain of said second linear amplifier.

Claim 18

Apparatus comprising: input means for supplying an angle-modulated carrier; limiter means including a plurality of cascaded limiter stages for successively amplifying said angle-modulated carrier for forming a pulse signal; information detector means for deriving an information signal in response to said pulse signal; first and second linear amplifier stages coupled in cascade beside at least a portion of said cascade of said limiter amplifier stages for amplifying an intermediate signal developed at an intermediate point in said cascade to develop an output signal, said first linear amplifier including a degenerative feedback path, said second linear amplifier including gain control means; detector means for generating an amplitude representative signal in response to said output signal having a magnitude representing the amplitude of said output signal; control means responsive to said amplitude representative signal for generating a main control signal having a magnitude substantially linearly related to the magnitude of said amplitude representative signal and an auxiliary control signal having a magnitude substantially non-linearly related to the magnitude of said amplitude representative signal; and utilization means for utilizing said main control signal; said auxiliary control signal being applied to said gain control means for degeneratively controlling the gain of said second linear amplifier.