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US 6,184,751 B2Granted
Amplifier circuit
AssigneeMotorola, Inc.
InventorsJohn Robert Siomkos, Edgar Herbert Callaway, Jr.
Life of this patent
Estimating the term…
Abstract
An amplifier circuit (20) uses a series transistor (38) to couple the output of an amplifier (26) to a tuned circuit load (40) and to act as a variable resistance. In one embodiment for a multi-band receiver, multiple series transistors (38, 42) are switched for connecting different tuned circuits (40, 44) to the amplifier's output, and an activated one of the series transistors receives a gate voltage that varies its resistance so as to achieve gain control. An activated series transistors can also provide a resistance that stabilizes the amplifier (26).
Claims7
A gain-controlled amplifier circuit for a multi-band receiver, comprising:
- an amplifier having an output;
- at least a first tuned circuit tuned to a first band of frequencies and a second tuned circuit tuned to a second band of frequencies;
- a first series transistor coupled between the output of the amplifier and the first tuned circuit;
- a second series transistor coupled between the output of the amplifier and the second tuned circuit, the first and second series transistors each having a gate and a source, and an activated one of the series transistors creating a series path of variable resistance between the output of the amplifier and a tuned circuit;
- band selection circuitry coupled to the first series transistor and to the second series transistor for selectively activating one of the first and second series transistors;
- and
- gain control circuitry coupled to an activated series transistor for varying a voltage Vgs between the gate and the source of the activated series transistor so as to vary the resistance of the activated series transistor.
4 more elements
A gain-controlled amplifier circuit for a multi-band receiver, comprising:
- a cascode amplifier having an output;
- parasitic capacitance coupled to the output of the amplifier;
- at least a first tuned circuit tuned to a first band of frequencies and a second tuned circuit tuned to a second band of frequencies;
- a first series transistor coupled between the output of the amplifier and the first tuned circuit;
- a second series transistor coupled between the output of the amplifier and the second tuned circuit, wherein the first and second series transistors each has a gate and a source, and wherein an activated one of the series transistors creates a series path of variable resistance between the output of the amplifier and a selected tuned circuit;
- band selection circuitry coupled to the first series transistor and to the second series transistor for selectively activating one of the first and second series transistors;
- a source of AGC current;
- and
- current mirror circuitry receiving the AGC current for applying a variable voltage to the gate of the activated series transistor, the variable voltage varying in response to variations in the AGC current, and wherein the activated series transistor acts as a low resistance when the variable voltage is at a low value to thereby cause the parasitic capacitance to be effectively coupled in parallel with the selected tuned circuit.
6 more elements
An amplifier circuit for a multi-band receiver, comprising:
- an amplifier having an output;
- at least a first tuned circuit tuned to a first band of frequencies and a second tuned circuit tuned to a second band of frequencies;
- a first series transistor coupled between the output of the amplifier and the first tuned circuit;
- a second series transistor coupled between the output of the amplifier and the second tuned circuit, wherein each of the series transistors has a gate, wherein an activated one of the series transistors creates a series path between the output of the amplifier and a tuned circuit, and wherein the first and second series transistors each exhibit a resistance that varies with the amplitude of a voltage received at its gate;
- band selection circuitry coupled to the first series transistor and to the second series transistor for selectively activating one of the first and second series transistors;
- a source of control current having at least a first maximum current level for the first band of frequencies and at least a second maximum current level for the second band of frequencies;
- and
- current mirror circuitry receiving the control current for supplying, to the gate of the activated series transistor, a voltage selected to cause the activated series transistor to exhibit a resistance that depends on the band of frequencies being received.
5 more elements
Dependencies are inferred from the claim text.