Miscellaneous active electrical nonlinear devices – circuits – and – Specific input to output function – Combining of plural signals
Reexamination Certificate
2001-07-11
2002-06-11
Tran, Toan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific input to output function
Combining of plural signals
C330S252000
Reexamination Certificate
active
06404263
ABSTRACT:
TECHNICAL FIELD
The present invention relates, in general, to mixers used in wireless communications systems and, more specifically, to a mixer that reduces the effect of the harmonics of the local oscillator signal, particularly the second harmonic.
BACKGROUND OF THE INVENTION
A “Gilbert Mixer” is widely used in radio frequency communications systems.
FIG. 1
is a circuit diagram of a conventional “Gilbert Mixer.” Mixer
10
includes a mixer core
13
, which includes transistors Q
1
, Q
2
, Q
3
, and Q
4
, and a radio frequency input section
15
, which includes transistors Q
5
and Q
6
.
The operation of mixer
10
is as follows. In the absence of any voltage difference between the base of transistor Q
5
and the base of transistor Q
6
, the collector currents of these two transistors are essentially equal. Thus, a voltage applied to the local oscillator port
12
results in no change of output current. Should a small DC offset voltage be present at the radio frequency port
14
(e.g., due to a mismatch in the emitter areas of transistors Q
5
and Q
6
), this will only result in a small feed through of the local oscillator signal V
LO
to the intermediate frequency output port
16
which will be blocked by a first intermediate frequency filter (not shown). Conversely, if a radio frequency signal V
RF
is applied to the radio frequency port
14
, but no voltage difference is applied to the local oscillator port
12
, the output currents will again be balanced. A small offset voltage (due now to emitter mismatch in transistors Q
1
, Q
2
, Q
3
, and Q
4
) may cause some radio frequency signal feed through to the intermediate frequency port
16
. As before, this will be rejected by the intermediate frequency filter. Thus, it is only when a signal supplied to both the local oscillator port
12
and the radio frequency port
14
that a signal appears at the intermediate frequency port
16
. To reduce the gain and increase the input linearity of the mixer
10
, a capacitor
18
and a resistor
20
are connected between the base and the collector of transistor Q
5
and a capacitor
22
and a resistor
24
are connected between the base and the collector of transistor Q
6
.
Of concern with such a mixer is the possibility of high second harmonic contents in the emitters of the quad transistors Q
1
, Q
2
, Q
3
, and Q
4
when the input level of the local oscillator signal is high. The presence of the second harmonic, which is of most concern because it has the greatest effect due to its magnitude when compared to the other harmonics, can degrade the conversion gain and linearity of the mixer.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a new and improved mixer for a wireless communications system.
Another object of the present invention is to provide a new and improved mixer for a wireless communications system that compensates for harmonics of the local oscillator signal, particularly the second harmonic.
A further object of the present invention is to provide a mixer for a wireless communications system that is relatively simple in construction and inexpensive to manufacture.
Accordingly, a mixer, constructed in accordance with the present invention, includes means for supplying a first input signal and means for supplying a second input signal. This mixer also includes an input section circuit responsive to the first input signal for translating the first input signal from a voltage signal to first and second current signals. The input section circuit includes (a) first and second transducers connected in a differential configuration and each having an output for supplying one of the first and second current signals, (b) a first reactance circuit connected between a first of the transducer outputs and ground, and (c) a second reactance circuit connected between a second of the transducer outputs and ground. A mixer, constructed in accordance with the present invention, further includes a mixer core circuit responsive to the first and second current signals and the second input signal for developing a differential mixed output signal that is the product of the current signals and the second input signal.
It is to be understood that the foregoing general description of the present invention and the following detailed description of the present invention are exemplary, but are not restrictive of the invention.
REFERENCES:
patent: 5329189 (1994-07-01), Ushida et al.
patent: 5379457 (1995-01-01), Nguyen
patent: 5565809 (1996-10-01), Shou et al.
patent: 5587682 (1996-12-01), Colli et al.
patent: 5589791 (1996-12-01), Gilbert
patent: 5625307 (1997-04-01), Scheinberg
patent: 5675392 (1997-10-01), Nayebi et al.
patent: 5844449 (1998-12-01), Abeno et al.
patent: 5847623 (1998-12-01), Hadjichristos
patent: 5973539 (1999-10-01), Komurasaki et al.
patent: 6054889 (2000-04-01), Kobayashi
patent: 6073002 (2000-06-01), Peterson
patent: 6118339 (2000-09-01), Gentzler et al.
Abate Esq. Joseph P.
Nguyen Linh
Tran Toan
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