Gain-variable amplifier circuit

Claim 2

A circuit for compensating for a frequency characteristic of a transmission signal transmitted through a transmission path having a predetermined transmission characteristic, comprising: first means, having a first predetermined frequency characteristic and a first predetermined amplification factor, for outputting a first signal obtained by changing an amplitude of the transmission signal with a first coefficient in accordance with a predetermined control signal; second means, having a second predetermined frequency characteristic and a second predetermined amplification factor, for outputting a second signal obtained by changing an amplitude of the transmission signal with a second coefficient, wherein the second predetermined frequency characteristic compensates for a characteristic depending on a length of said transmission path, and a magnitude of the second coefficient is reduced when a magnitude of the first coefficient is increased and increased when the magnitude of the first coefficient is reduced; and synthesizing means, coupled to said first and second means, for outputting a synthesized signal of the first signal and the second signal.

Claim 3

A circuit according to claim 1, wherein said transmission path has an attenuation frequency characteristic of attenuating the transmission signal in substantially inverse proportion to √f where f is the frequency of the transmission signal, and the first predetermined frequency characteristic defined within a given compensation frequency range in which the attenuation frequency characteristic is to be compensated for is substantially flat.

Claim 4

A circuit according to claim 2, wherein the second predetermined frequency characteristic within the compensation frequency range has a frequency characteristic of increasing the transmission signal substantially in proportion to the √f.

Claim 5

A circuit according to claim 3, wherein said second means includes: means for setting a ratio between the first predetermined amplification factor, at a predetermined frequency portion of the first predetermined frequency characteristic, and the second predetermined amplification factor, at the predetermined frequency portion of the second predetermined frequency characteristic, to be a predetermined value.

Claim 6

A circuit according to claim 2, wherein said second means includes: switch means for selecting, as the second predetermined frequency characteristic within the compensation frequency range, from either a substantially flat frequency characteristic or a frequency characteristic of increasing the transmission signal in proportion to the √f.

Claim 7

A circuit according to claim 2, wherein the first and second coefficients are determined such that a sum of the first coefficient and the second coefficient becomes substantially a predetermined constant value.

Claim 8

A circuit according to claim 6, wherein said synthesizing means includes: means for adding the second signal to the first signal to provide the synthetic signal.

Claim 9

A compensating circuit for a transmission signal transmitted through a transmission path having a predetermined transmission characteristic, comprising: first circuit means for amplifying the transmission signal with a frequency characteristic of compensating an amplitude attenuation of the transmission signal, and outputting a first current signal; second circuit means for amplifying the transmission signal with a predetermined frequency characteristic and outputting a second current signal; load means, connected to a power source circuit, for producing an output signal corresponding to the transmission signal; a first transistor having an emitter for receiving the first current signal, a base for receiving a first control signal, and a collector coupled to said power source circuit via said load means; a second transistor having an emitter for receiving the first current signal, a base for receiving a second control signal whose level change phase is opposite to a level change phase of the first control signal, and a collector connected to said power source circuit; a third transistor having an emitter for receiving the second current signal, a base for receiving the first control signal, and a collector connected to said power source circuit; and a fourth transistor having an emitter for receiving the second current signal, a base for receiving the second control signal, and a collector coupled to said power source circuit via said load means.

Claim 10

A compensating circuit for a transmission signal transmitted through a transmission path having a predetermined transmission characteristic, comprising: first circuit means for amplifying the transmission signal with a frequency characteristic of compensating an amplitude attenuation of the transmission signal, and outputting a first current signal; second circuit means for amplifying the transmission signal with a predetermined frequency characteristic and outputting a second current signal; load means, connected to a power source circuit, for producing an output signal corresponding to the transmission signal; a first transistor having an emitter for receiving the first current signal, a base for receiving a first control signal, and a collector coupled to said power source circuit via said load means; a second transistor having an emitter for receiving the first current signal, a base for receiving a second control signal whose level change phase is opposite to a level change phase of the first control signal, and a collector connected to said power source circuit; a third transistor having an emitter for receiving the second current signal, a base for receiving the first control signal, and a collector connected to said power source circuit; and a fourth transistor having an emitter for receiving the second current signal, a base for receiving the second control signal, and a collector coupled to said power source circuit via said load means.

Claim 11

A compensating circuit for a balanced transmission signal, comprising: first balanced circuit means for amplifying the balanced transmission signal with a frequency characteristic of compensating an amplitude attenuation, and outputting a pair of first balanced current signals; second balanced circuit means for amplifying the balanced transmission signal with a predetermined frequency characteristic, and outputting a pair of second balanced current signals; first load means, connected to a power source circuit, for supplying a first output signal corresponding to the balanced transmission signal; second load means, connected to said power source circuit, for supplying a second output signal having a phase opposite to that of the first output signal; a first transistor having an emitter for receiving one of the first balanced current signals, a base for receiving a first control signal, and a collector coupled to said power source circuit via said first load means; a second transistor having an emitter for receiving one of the first balanced current signals, a base for receiving a second control signal whose level change phase is opposite to a level change phase of the first control signal, and a collector connected to said power source circuit; a third transistor having an emitter for receiving the other of the first balanced current signals, a base for receiving the second control signal, and a collector connected to said power source circuit; a fourth transistor having an emitter for receiving the other of the first balanced current signals, a base for receiving the first control signal, and a collector connected to said power source circuit via said second load means; a fifth transistor having an emitter for receiving one of the second balanced current signals, a base for receiving the first control signal, and a collector connected to said power source circuit; a sixth transistor having an emitter for receiving one of the second balanced current signals, a base for receiving the second control signal, and a collector coupled to said power source circuit via said first load means; a seventh transistor having an emitter for receiving the other of the second balanced current signals, a base for receiving the second control signal, and a collector coupled to said power source circuit via said second load means; and an eighth transistor having an emitter for receiving the other of the second balanced current signals, a base for receiving the first control signal, and a collector connected to said power source circuit.

Claim 12

A compensating circuit for a balanced transmission signal, comprising: first balanced circuit means for amplifying the balanced transmission signal with a frequency characteristic of compensating an amplitude attenuation, and outputting a pair of first balanced current signals; second balanced circuit means for amplifying the balanced transmission signal with a predetermined frequency characteristic, and outputting a pair of second balanced current signals; first load means, connected to a power source circuit, for supplying a first output signal corresponding to the balanced transmission signal; second load means, connected to said power source circuit, for supplying a second output signal having a phase opposite to that of the first output signal; a first transistor having an emitter for receiving one of the first balanced current signals, a base for receiving a first control signal, and a collector coupled to said power source circuit via said first load means; a second transistor having an emitter for receiving one of the first balanced current signals, a base for receiving a second control signal whose level change phase is opposite to a level change phase of the first control signal, and a collector connected to said power source circuit; a third transistor having an emitter for receiving the other of the first balanced current signals, a base for receiving the second control signal, and a collector connected to said power source circuit; a fourth transistor having an emitter for receiving the other of the first balanced current signals, a base for receiving the first control signal, and a collector connected to said power source circuit via said second load means; a fifth transistor having an emitter for receiving one of the second balanced current signals, a base for receiving the first control signal, and a collector connected to said power source circuit; a sixth transistor having an emitter for receiving one of the second balanced current signals, a base for receiving the second control signal, and a collector coupled to said power source circuit via said first load means; a seventh transistor having an emitter for receiving the other of the second balanced current signals, a base for receiving the second control signal, and a collector coupled to said power source circuit via said second load means; and an eighth transistor having an emitter for receiving the other of the second balanced current signals, a base for receiving the first control signal, and a collector connected to said power source circuit.

Claim 13

A variable gain amplifier for compensating for an amplitude frequency response characteristic of a transmission signal transmitted through a transmission path having a predetermined attenuation characteristic, comprising: first amplifying means, having a first predetermined frequency characteristic, for amplifying the transmission signal and outputting a first amplified signal; second amplifying means, having a second predetermined frequency characteristic, for amplifying the transmission signal and outputting a second amplified signal, wherein the second predetermined frequency characteristic has a high-frequency range increasing characteristic of compensating for the attenuation characteristic which is changed by a length of said transmission path; first amplitude changing means, connected to said first amplifying means, for outputting a first change signal obtained by changing an amplitude of the first amplified signal with a first coefficient in accordance with a predetermined control signal; second amplitude changing means, connected to said second amplifying means, for outputting a second change signal obtained by changing an amplitude of the second amplified signal with a second coefficient in accordance with the predetermined control signal, wherein a magnitude of the second coefficient is reduced when a magnitude of the first coefficient is increased and increased when the magnitude of the first coefficient is reduced; and means, connected to said first and second amplitude changing means, for providing an output signal obtained by combining the first change signal with the second change signal.

Claim 14

A variable gain amplifier for compensating for an amplitude frequency response characteristic of a transmission signal transmitted through a transmission path having a predetermined attenuation characteristic, comprising: first amplifying means, having a first predetermined frequency characteristic, for amplifying the transmission signal and outputting a first amplified signal; second amplifying means, having a second predetermined frequency characteristic, for amplifying the transmission signal and outputting a second amplified signal, wherein the second predetermined frequency characteristic has a high-frequency range increasing characteristic of compensating for the attenuation characteristic which is changed by a length of said transmission path; first amplitude changing means, connected to said first amplifying means, for outputting a first change signal obtained by changing an amplitude of the first amplified signal with a first coefficient in accordance with a predetermined control signal; second amplitude changing means, connected to said second amplifying means, for outputting a second change signal obtained by changing an amplitude of the second amplified signal with a second coefficient in accordance with the predetermined control signal, wherein a magnitude of the second coefficient is reduced when a magnitude of the first coefficient is increased and increased when the magnitude of the first coefficient is reduced; and means, connected to said first and second amplitude changing means, for providing an output signal obtained by combining the first change signal with the second change signal.

Claim 15

A compensating apparatus for automatically compensating for a frequency characteristic of a trans mission signal transmitted through a transmission path having a predetermined transmission characteristic, comprising: (a) a first compensating circuit including: first means, having a first predetermined frequency characteristic and a first predetermined amplification factor, for outputting a first signal obtained by changing an amplitude of the transmission signal with a first coefficient in accordance with a predetermined control signal; second means, having a second predetermined frequency characteristic and a second predetermined amplification factor, for outputting a second signal obtained by changing the amplitude of the transmission signal with a second coefficient in accordance with the predetermined control signal, wherein the second predetermined frequency characteristic has a characteristic of compensating for a characteristic depending on said transmission path, and a magnitude of the second coefficient is reduced when a magnitude of the first coefficient is increased and increased when the magnitude of the first coefficient is reduced; and first synthesizing means, connected to said first and second means, for synthesizing the first and second signals and supplying a first output signal; (b) a second compensating circuit connected to said first compensating circuit, including: third means, having a third predetermined frequency characteristic and a third predetermined amplification factor, for outputting a third signal obtained by changing an amplitude of the first output signal with the first coefficient in accordance with the predetermined control signal; fourth means, having a fourth predetermined frequency characteristic and a fourth predetermined amplification factor, for outputting a fourth signal obtained by changing the amplitude of the first output signal with the second coefficient in accordance with the predetermined control signal, wherein the fourth predetermined frequency characteristic has a characteristic of compensating for the characteristic depending on said transmission path; and second synthesizing means, connected to said third and fourth means, for synthesizing the third and fourth signals and supplying a second output signal; and (c) a coefficient controller, connected to said second compensating circuit, for supplying a compensation output corresponding to the second output signal, and generating, as the predetermined control signal, a signal corresponding to a difference between a signal level of the compensation output and a predetermined reference level.

Claim 16

A compensating apparatus for automatically compensating for a frequency characteristic of a trans mission signal transmitted through a transmission path having a predetermined transmission characteristic, comprising: (a) a first compensating circuit including: first means, having a first predetermined frequency characteristic and a first predetermined amplification factor, for outputting a first signal obtained by changing an amplitude of the transmission signal with a first coefficient in accordance with a predetermined control signal; second means, having a second predetermined frequency characteristic and a second predetermined amplification factor, for outputting a second signal obtained by changing the amplitude of the transmission signal with a second coefficient in accordance with the predetermined control signal, wherein the second predetermined frequency characteristic has a characteristic of compensating for a characteristic depending on said transmission path, and a magnitude of the second coefficient is reduced when a magnitude of the first coefficient is increased and increased when the magnitude of the first coefficient is reduced; and first synthesizing means, connected to said first and second means, for synthesizing the first and second signals and supplying a first output signal; (b) a second compensating circuit connected to said first compensating circuit, including: third means, having a third predetermined frequency characteristic and a third predetermined amplification factor, for outputting a third signal obtained by changing an amplitude of the first output signal with the first coefficient in accordance with the predetermined control signal; fourth means, having a fourth predetermined frequency characteristic and a fourth predetermined amplification factor, for outputting a fourth signal obtained by changing the amplitude of the first output signal with the second coefficient in accordance with the predetermined control signal, wherein the fourth predetermined frequency characteristic has a characteristic of compensating for the characteristic depending on said transmission path; and second synthesizing means, connected to said third and fourth means, for synthesizing the third and fourth signals and supplying a second output signal; and (c) a coefficient controller, connected to said second compensating circuit, for supplying a compensation output corresponding to the second output signal, and generating, as the predetermined control signal, a signal corresponding to a difference between a signal level of the compensation output and a predetermined reference level.

Claim 17

A variable gain amplifier for compensating for an amplitude frequency response characteristic of a signal transmitted through a transmission path having a predetermined attenuation characteristic, comprising: a first amplifier for amplifying a signal transmitted through said transmission path and having a substantially flat amplitude frequency response characteristic, and providing a first output signal; a second amplifier for amplifying a signal transmitted through said transmission path and having a predetermined amplitude frequency response characteristic corresponding to an attenuation characteristic of said transmission path, and providing a second output signal; an adder circuit for reciprocally level-controlling the first and second output signals from said first and second amplifiers, so that a level of one of the first and second output signals is increased when a level of the other thereof is reduced, and adding the level controlled first and second output signals to each other; and an addition controller for variably setting an amount of the level control performed by said adder circuit in accordance with a line length of said transmission path.

Claim 18

A variable gain amplifier for compensating for an amplitude frequency response characteristic of a signal transmitted through a transmission path having a predetermined attenuation characteristic, comprising: a first amplifier for amplifying a signal transmitted through said transmission path and having a substantially flat amplitude frequency response characteristic, and providing a first output signal; a second amplifier for amplifying a signal transmitted through said transmission path and having a predetermined amplitude frequency response characteristic corresponding to an attenuation characteristic of said transmission path, and providing a second output signal; an adder circuit for reciprocally level-controlling the first and second output signals from said first and second amplifiers, so that a level of one of the first and second output signals is increased when a level of the other thereof is reduced, and adding the level controlled first and second output signals to each other; and an addition controller for variably setting an amount of the level control performed by said adder circuit in accordance with a line length of said transmission path.

Claim 19

An amplifier according to claim 12, wherein said second amplifier has as its amplitude frequency response characteristic a first characteristic obtained by approximating the attenuation characteristic of said transmission path and a second characteristic which is substantially flat, and includes means for selectively setting one of the first and second characteristics in accordance with a type of said transmission path.