Low noise active mixer
AssigneeHewlett-Packard Company
InventorNhat M. Nguyen
Life of this patent
Estimating the term…
Abstract
In a conventional Gilbert-cell active mixer, two local oscillator matched pairs of transistors receive a local oscillator input signal and are coupled to a radio frequency matched pair of transistors which receive a radio frequency input signal. The circuit generates an intermodulated output signal at the collectors of the local oscillator matched pairs. Noise degradation is reduced over the conventional mixer by replacing the standard radio frequency emitter degeneration resistor with a reactive element, thereby reducing thermal noise. Narrow-band input matching is achieved by insertion of a series inductive element and optional parallel capacitive element in line with the radio frequency input. Thermal noise contributed to the circuit is thereby minimized while circuit linearity is preserved in the narrow frequency band of interest.
Claims18
An active mixer circuit comprising:
- a first local oscillator matched pair of transistors;
- a second local oscillator matched pair of transistors having operating characteristics approximately the same as the operating characteristics of the first local oscillator matched pair;
- a radio frequency matched pair of transistors;
- means for coupling the first local oscillator pair of transistors to one of the transistors of the radio frequency pair;
- means for coupling the second local oscillator pair of transistors to the other transistor of the radio frequency pair;
- means for reactively coupling the two transistors of the radio frequency pair, said reactive coupling means comprising an inductor;
- a local oscillator input coupled to control terminals of the local oscillator pairs of transistors;
- and
- a radio frequency input coupled to control terminals of the radio frequency pair of transistors.
An active mixer circuit comprising:
- a first local oscillator matched pair of bipolar transistors;
- a second local oscillator matched pair of bipolar transistors having operating characteristics approximately the same as the operating characteristics of the first local oscillator matched pair;
- a radio frequency matched pair of bipolar transistors;
- means for coupling the emitters of the first local oscillator pair to the collector of one of the transistors of the radio frequency pair;
- means for coupling the emitters of the second local oscillator pair to the collector of the other transistor of the radio frequency pair;
- means for inductively coupling the emitters of the two transistors of the radio frequency pair;
- a local oscillator input coupled to the bases of the local oscillator matched pairs;
- and
- a radio frequency input coupled to the bases of the radio frequency matched pair.
In a conventional double-balanced Gilbert-cell active mixer comprising a matched radio frequency differential pair of transistors, the improvement comprising:
- means for reactive emitter degeneration of the radio frequency pair of transistors;
- and
- reactive means for matching an input impedance of the radio frequency differential pair to an output impedance of a radio frequency input to the mixer, and wherein
- the emitter degeneration means includes an inductor for improving the noise performance of the Gilbert-cell active Mixer.
Dependencies are inferred from the claim text.