INTERMODULATION REJECTION CAPABILITIES OF FIELD-EFFECT TRANSISTOR RADIO FREQUENCY AMPLIFIERS AND MIXERS

• US 3,716,730 A
• Filed: 04/19/1971
• Issued: 02/13/1973
• Est. Priority Date: 04/19/1971
• Status: Expired due to Term

• Current Assignee: Frank J. Cerny Jr
• Original Assignee: Frank J. Cerny Jr
• Inventors: Cerny, Frank J. Jr.
• Primary Examiner(s): Lake, Roy
• Assistant Examiner(s): Mullins, James B.
• Application Number:
  US05/135,278
• Time in Patent Office: 666 Days
• Field of Search: 330/35 325/436,451 307/304,295
• US Class Current: 327/113
• CPC Class Codes: H03D 7/125 with field effect transistors
• CPC Class Codes: H03F 2203/21178 Power transistors are made by coupling a plurality of single transistors in parallel
• CPC Class Codes: H03F 3/04 with semiconductor devices only
• CPC Class Codes: H03F 3/1935 with junction-FET devices
• CPC Class Codes: H03F 3/211 using a combination of several amplifiers H03F3/60 takes precedence

Abstract

Mixers and amplifier circuits are disclosed which may include a plurality of identical FETs connected in parallel to form a composite FET. The decreased input impedance of the composite FET as compared to the input impedance of a single FET results in a decrease in intermodulation. The composite FET may also be a power or large signal FET. In either case, the pinch-off voltage of the composite FET can also be increased to provide a still further decrease in intermodulation.

Claims

1. A radio frequency mixer suitable for use in a communications receiver and developing a desired output signal of a frequency which is a function of the frequency of a desired small amplitude input signal and of the frequency of a mixing signal, the radio frequency mixer tending to prevent intermodulation between undesired input signals and including in combination:

field-effect transistor means having a source-to-drain semiconductor structure with source and drain terminals electrically connected thereto and a gate structure with a gate terminal electrically connected thereto, said source-to-drain structure having selected dimensions and doping which causes the gate pinch-off voltage of said field-effect transistor means to be at least 20% greater than the pinch-off voltage of a standard, small signal field-effect transistor, said fieldeffect transistor means reducing the magnitude of the current through said source-to-drain structure and between said source and drain terminals to substantially zero in response to a reverse bias voltage applied between said gate and source terminals equal to said increased gate pinch-off voltage;

first signal supply means having a first output terminal connected to said gate terminal and a second output terminal, first circuit means connecting said second output terminal to said source terminal, said first signal supply means providing to said gate terminal the desired input signal having a particular frequency which may be accompanied by undesired input signals having other frequencies which differ from said particular frequency;

second signal supply means having a first output terminal connected to said source terminal and a second output terminal, second circuit means connecting said second output terminal of said second signal supply means to said gate terminal, said second signal supply means developing the mixing signal of a predetermined frequency which is different from said particular frequency of the desired input signal across said gate and source terminals;

said gate structure and said source-to-drain structure of said field-effect transistor means being responsive to said desired input signal and said mixing signal to produce the desired output signal in said source-to-drain structure which has a frequency that is a function of the frequencies of the desired input signal and the mixing signal, said undesired signals tending to intermodulate within said structure of said fieldeffect transistor means to provide an undesired intermodulation signal at the frequency of the desired output signal; and

said source-to-drain structure and said gate structure of said field-effect transistor means cooperating to hold the magnitude of said undesired intermodulation signal at a reduced magnitude as a result of said increased pinch-off voltage as compared to the magnitude of an undesired intermodulation signal provided by a standard, small signal field-effect transistor operating under the same conditions.

2. The field-effect transistor radio frequency mixer of claiM 1 wherein said source-to-drain structure is constructed to allow a source-to-drain current in excess of 50 milliamperes to flow between said source and drain terminals in response to source-to-drain voltages in excess of said gate pinch-off voltage and to said gate terminal being shorted to said source terminal to further decrease the magnitude of said undesired intermodulation signal.

3. The field-effect radio frequency mixer stage of claim 2 wherein said source-to-drain structure provides a channel having an effective width on the order of 126 thousandths of an inch, said channel conducting substantially greater source-to-drain current than a standard small signal field-effect transistor to thereby facilitate intermodulation rejections on the order of 90 decibels.

4. The radio frequency mixer of claim 1 wherein said field-effect transistor means includes at least one field-effect transistor having a gate pinch-off voltage in excess of 10 volts.

5. The radio frequency mixer of claim 4 wherein said field-effect transistor means includes a plurality of said field-effect transistors each having said gate pinch-off voltage in excess of 10 volts connected in parallel.

6. The radio frequency mixer of claim 5 wherein said plurality of field-effect transistors are connected in parallel in a common-source configuration.

7. The radio frequency mixer of claim 5 wherein said plurality of field-effect transistors are connected in parallel in a common-gate configuration.

8. A radio frequency mixer suitable for use in a communications receiver and developing a desired output signal of a frequency which is a function of the frequency of a desired small amplitude input signal and of the frequency of a mixing signal, the radio frequency mixer providing a high rejection of intermodulation between undesired input signals and including in combination:

field-effect transistor means having a source-to-drain semiconductor structure with source and drain terminals electrically connected thereto and a gate structure with a gate terminal electrically connected thereto, said source-to-drain structure having selected dimensions and doping which establish a gate pinch-off voltage and which allow a source-to-drain current in excess of 50 milliamperes to flow between said source and drain terminals in response to source-to-drain voltages in excess of said gate pinch-off voltage;

first signal supply means having a first output terminal connected to said gate terminal and a second output terminal, first circuit means connecting said second output terminal to said source terminal, said first signal supply means providing to said gate terminal the desired input signal having a particular frequency which may be accompanied by undesired input signals having other frequencies which differ from said particular frequency;

second signal supply means having a first output terminal connected to said source terminal and a second output terminal, second circuit means connecting said second output terminal of said second signal supply means to said gate terminal, said second signal supply means developing the mixing signal of a predetermined frequency which is different from said particular frequency of the desired input signal across said gate and source terminals;

said gate structure and said source-to-drain structure of said field-effect transistor means being responsive to said desired input signal and said mixing signal to produce the desired output signal in said source-to-drain structure which has a frequency that is a function of the frequencies of the desired input signal and the mixing signal, said undesired signals tending to intermodulate within said structure of said field-effect transistor means to provide an undesired intermodulation signal at the frequency of the desired output signal; and

said source-to-drain structure and said gate structure of said field-effect transistor means cooperating to decrease the magnitude of saiD undesired intermodulation signal as a result of said selected dimensions and doping.