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High dynamic range mixer
| Details |
Inventors: Jaffer, Aubrey;
Assignee:
Primary Examiner: Masinick; Michael A.
Assistant Examiner:
Attorney, Agent or Firm: Weingarten, Schurgin, Gagnebin & Hayes
A high performance, double-balanced mixer comprising a novel transformer and a pair of variable conductance semiconductor devices connected thereto which provides an output signal being the product of two input signals. Two transformer windings each include a center tap which together form one port of the mixer. Each variable conductance devices provides a selected conductivity path across the end of one of the center tapped windings to the beginning of the other center tapped winding. A second port signal provided oppositely modulates the variable conductance devices to provide a decrease in conductivity across one path while increasing the conductivity of the other path. The third winding of the transformer provides a third port to the mixer. A singularly-balanced mixer embodiment is shown. The mixer according to the present invention is operable to provide vastly improved linearity for either of two inputs as well as low noise and wide bandwidth operation. |
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DETAILED DESCRIPTION OF THE PRESENT INVENTION A schematic diagram 50 of FIG.
1 showing one embodiment of the doubly-balanced mixer according to the present invention, comprises a transformer 60 having three windings 62, 64 and 66, shown having the beginning end indicated by a dot.
Windings 64 and 66 are provided with center taps, which together form a port and across which a balanced signal input or output may be connected at 52.
The beginning of winding 64 is connected to the end of winding 66 through a variable conductance element; similarly, the beginning of winding 66 connected to the end of winding 64 through a second variable conductance element.
In the embodiment shown in FIG.
1, these variable conductance elements comprise field effect transistors (FETs) 70 and 72, respectively.
In the same manner that the center tap of winding 64 and 66 form one port of the mixer, another port at 56 receives a balanced signal source 57, and a port 54 is connected to the third winding 62.
The port at 56 can only serve as a signal input port as it serves to excite or control the variable conductance elements, FETs 70 and 72, respectively.
Since the FETs 70 and 72 typically require bias potential for conduction through all levels of the signal imposed thereon, a bias potential is necessarily developed thereacross.
The bias voltage V.
sub.
0 is applied across the center of the exciting source 57 and the source or output at 52.
The bias potential may be selected according to the operating characteristics of the field effect transistors 70 and 72, to maintain them in a selected conductivity range throughout the modulation of signal source 56 and may be used to select or control the impedance of the mixer 50.
Since the present invention provides a constant total conductivity for both FETs 70 and 72, the impedance of the mixer is controlled by the conductivity of the FETs 70 and 72, and thus the bias (e.
g.
, by adjusting 110 of FIG.
4).
The third winding 62 is connected to a signal source or provides an output 55 at 54
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