GALLIUM-ARSENIDE SWITCHING MIXER

Abstract: A GaAs switching mixer (10) receives an information signal (16) and an injection signal (20) to provide an intermediate frequency signal. The injection signal (20) controls enhancement mode GaAs devices (18 and 22) so as to minimize the required injection drive level and harmonic distortion.

Description: GALLIUM-ARSENIDE SWITCHING MIXER Technical Field This invention relates generally to mixers, and more specifically to gallium-arsenide (GaAs) switching mixers, and is particularly directed toward a GaAs switching mixer employing enhancement mode GaAs switching devices. Background Art It is known that the distortion products generated in a switching mixer are proportional to the rise time of the injection signal provided by a local oscillator as well as by the other parameters some of which are internal to the devices in the mixer. Therefore, these distortion products can be minimized by reducing the injection signal's rise time. Known designs of GaAs switching mixers have attempted to vary device geometries of GaAs depletion mode devices to minimize the turn-on (switching point) of the devices. While helpful, such variation of depletion mode GaAs devices has not been able to satisfactorily reduce the required local oscillator drive level or harmonic distortion. Accordingly, a need exists for a superior GaAs switching mixer. Summary of the Invention Accordingly, it is an object of the present invention to provide a GaAs mixer that overcomes the detriments of the prior art. The absolute value of threshold voltages in GaAs enhancement mode devices is significantly less than the absolute value of pinchoff voltages in depletion mode devices. Thus, according to the invention, a GaAs switching mixer receives an information signal and an injection signal to provide an intermediate frequency signal. The injection signal controls enhancement mode GaAs devices so as to minimize the required injection drive level and distortion products. Brief Description of the Drawings Figure 1 illustrates a GaAs mixer in accordance with the present invention. Detailed Description of the Preferred Embodiment Referring to Figure 1, a switching mixer circuit 10 is arranged in what is commonly known as a double-balanced mixer configuration. A current source 12 is coupled from the sources of a differential pair of gallium-arsenide depletion mode field effect transistors 14 and 14' to ground. Transistors 14 and 14' are coupled in what is known as a single-balanced configuration. Thus, the source of transistor 14 is coupled to the source of transistor 14'. The drain of transistor 14 is coupled to the sources of a differential pair of enhancement mode galiium-arsenide transistors 18 and 22 and the drain of transistor 14' is coupled to the sources of the differential pair of transistors 18' and 22'. Transistors 14 and 14' are as close to being geometrically symmetrical as possible, as are the 18 and 18' transistors and 22 and 22 * transistors, respectively. The drain of transistor 18 is coupled to a primary terminal 26 of transformer coupling 24 and the drain of transistor 18' is coupled to the opposite primary terminal 26' of transformer coupling 24. The drain of transistor 22 is coupled to the drain of transistor 18' and, similarly, the drain of transistor 22' is coupled to the drain transistor 18. The primary winding of transformer 24 is center-tapped at terminal 28 to provide a balanced output. The secondary coupling of transformer 24 extends between terminals 30 and 30'. Radio-frequency information signal 16 is applied to the gate of transistor 14 and radio-frequency signal 16' (i.e., the compliment or negative of signal 16') is applied to the gate of transistor 14'. Signals 16 and 16' are known as complementary-phased signals. A local oscillator injection signal 20 is applied to the gates of transistors 18 and 18'. Signal 20', (the complement of signal 20) is applied to the gates of transistors 22 and 22'. The complementary-phased signals 16, 16' cause the source currents in differential pairs 18, 22 and 18', 22' to vary. Thus, multiplication of complementary-phased signals 16, 16' and complementary-phased signals 20, 20' is accomplished in each of the differential pairs 18, 22 and 18', 22'. The output signal appears between terminals 30 and 30'. What is claimed is:

Claims: Claims 1. A gailium-arsenide switching mixer comprising : means for receiving an information signal; means for receiving an injection signal, coupled to said means for receiving an information signal, said means for receiving an injection signal including an enhancement mode gallium-arsenide transistor; whereby, the gallium-arsenide switching mixer operates to provide an output signal representing sum and difference frequencies . 2. A gallium-arsenide switching mixer comprising : means for receiving an information signal; means for receiving an injection signal, coupled to said means for receiving an information signal, said means for receiving an injection signal including at least two enhancement mode gallium-arsenide transistors coupled in a single-balanced configuration; whereby, the gallium-arsenide switching mixer operates to provide an output signal representing sum and difference frequencies . 3. A gallium-arsenide switching mixer comprising : means for receiving an information signal; means for receiving an injection signal, coupled to said means for receiving an information signal, said means for receiving an injection signal including at least four enhancement mode gallium-arsenide transistors coupled in a double-balanced configuration; whereby, the gallium-arsenide switching mixer operates to provide an output signal representing sum and difference frequencies . 4. The mixer of claim 1 , wherein the means for providing an information signal includes a pair of transistors. 5. The mixer of claim 1 , further comprising a means for providing a balanced output. 6. The mixer of claim 1 , wherein the means for providing an information signal includes a pair of depletion mode transistors. 7. The mixer of claim 2, wherein the means for providing an information signal includes a pair of transistors. 8. The mixer of claim 2, further comprising a means for providing a balanced output. 9. The mixer of claim 2, wherein the means for providing an information signal includes a pair of depletion mode transistors. 10. The mixer of claim 2, wherein the means for providing an information signal includes a pair of enhancement mode transistors. 11. The mixer of claim 3, wherein the means for providing an information signal includes a pair of transistors. 12. The mixer of claim 3, further comprising a means for providing a balanced output. 13. The mixer of claim 3, wherein the means for providing an information signal includes a pair of depletion mode transistors. 14. The mixer of claim 3, wherein the means for providing an information signal includes a pair of gallium-arsenide depletion mode transistors. 15. The mixer of claim 3, wherein the means for providing an information signal includes a pair of enhancement mode transistors. 16. The mixer of claim 3, wherein the means for providing an information signal includes a pair of gallium-arsenide enhancement mode transistors. 17. The mixer of claim 6, further comprising a means for providing a balanced output. 18. The mixer of claim 9, further comprising a means for providing a balanced output. 19. The mixer of claim 14, further comprising a means for providing a balanced output. 20. The mixer of claim 16, further comprising a means for providing a balanced output.

Inventors: CLARK EDWARD T, PRIETO YOLANDA, SIMMONS JOHN W, CLARK, EDWARD, T., PRIETO, YOLANDA, SIMMONS, JOHN, W.
Applicants: MOTOROLA INC, MOTOROLA, INC.
Application year: 1990
Main classification: B01F
IPC codes: H03D7, H04H1, H04H40