Gain-controlled amplifier using a controllable alternating-current resistance

A gain-controlled amplifier comprising:

• a source of control current;
• amplifier means including biasing means and an amplifying transistor, said amplifying transistor having base, emitter and collector electrodes and being biased for amplifying alternating current signals occupying a given range of frequencies;
• said base and emitter electrodes comprising a signal input circuit of said amplifying transistor, and said collector and emitter electrodes comprising a signal output circuit from which amplified signals are provided;
• and
• a vertical PNP transistor including a base-emitter junction which exhibits a resistance, the magnitude of which is controlled by said control current, including
• a semiconductor substrate of P type conductivity semiconductor material having a substantially planar surface;
• a first localized region of N type semiconductor material having a low concentration of conductivity modifiers, located in said substrate adjacent to the surface thereof, and exhibiting a carrier lifetime which is greater than the period of any one of said frequencies of said given range of frequencies;
• a second localized region of P type conductivity located in said first localized region adjacent to said surface, coupled to receive control current from said source, and containing P type conductivity modifiers having a concentration which is greater than said low concentration;
• and
• a third localized region of N type conductivity located in said first localized region, coupled to one of said electrodes of said signal output circuit of said amplifying transistor, and separated from said second localized region by an expanse of said first localized region, said third region containing N type conductivity modifiers having a concentration which is greater than said low concentration,
• wherein said third localized region comprises a base contact region, said base-emitter junction includes said first and second localized regions, and the resistance of said base-emitter junction is a function of the control current applied to said second localized region.

A gain-controlled amplifier comprising;

• a source of variable D.C. control current;
• a semiconductor substrate of one type conductivity and an epitaxial layer of opposite type conductivity with an interface therebetween, said epitaxial layer having a substantially planar surface;
• a first localized region of said opposite type conductivity located in said substrate adjacent to said interface and containing opposite type conductivity modifiers;
• a second localized region of said one type conductivity located in said epitaxial layer between said planar surface and said first localized region;
• a third localized region of said opposite type conductivity located in said second localized region adjacent to said planar surface and containing opposite type conductivity modifiers,
• a fourth localized region of said opposite type conductivity located in said epitaxial layer between said planar surface and said first localized region and containing opposite type conductivity modifiers;
• wherein said third localized region, said second localized region, and said epitaxial layer respectively comprise emitter, base and collector regions of an amplifying transistor, and said fourth region comprises a collector contact region of said transistor;
• means for applying an information signal to one of said base and emitter regions for producing an amplified information signal at said collector contact region;
• and
• variable impedance means coupled to said collector region and including a fifth localized region of said one type conductivity located in said epitaxial layer between said planar surface and said substrate and coupled to receive variable D.C. control current from said source, and containing one type conductivity modifiers, said fifth region being separated from said fourth region by an expanse of said epitaxial layer, said received D.C. control current causing an injection of carriers into said epitaxial layer expanse from said fifth region for variably controlling the impedance of said epitaxial layer expanse and the degree of amplification of said information signal.