Telecommunications – Receiver or analog modulated signal frequency converter – Frequency modifying or conversion
Reexamination Certificate
1998-12-08
2001-02-20
Eisenzopf, Reinhard (Department: 2682)
Telecommunications
Receiver or analog modulated signal frequency converter
Frequency modifying or conversion
C455S331000
Reexamination Certificate
active
06192229
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a diode mixer circuit for mixing a first and a second input signal. The invention also relates to a receiver in which a reception signal and a beat signal are mixed so as to obtain an intermediate frequency signal.
BACKGROUND OF THE INVENTION
The book entitled “High-Frequency Circuit Design” by James K. Hardy, Preston Publishing Company, 1979, pp. 317-318, describes mixer circuits. The FIG.
10
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) of this book shows a mixer circuit having a double-balance structure (double balanced mixer). The circuit includes four diodes which are connected so that they form a ring. The diode ring receives a radio-frequency signal (RF) and an oscillator signal (OSC) via a transformer. An intermediate frequency signal (IF) is obtained via another transformer. Thanks to the double-balance structure, relatively little remains of the oscillator signal in the intermediate frequency signal.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a diode mixer circuit which allows of a larger variety of applications.
The invention takes the following aspects into consideration. In the prior art, each transformer should process signals in a substantially symmetrical manner and without too many losses, for the mixer circuit to have a satisfactory performance. The manufacturing of a transformer requires special materials and a relatively complex method. Moreover, such a transformer is to have certain minimum dimensions; the transformer cannot be miniaturized at will without degrading its performance. Thus, the transformer is a relatively costly and relatively bulky element. In consequence, the mixer circuit according to the prior art is not suitable for use in low-cost applications such as, for example, in the field of consumer electronics. Neither is it suitable for miniature applications such as, for example, portable receivers.
According to the invention, a diode mixer circuit comprises a driving circuit for producing a first, second, third and fourth drive signal. Each drive signal is a combination of a first and a second input signal. The first and the second input signal (LO, RF) have the following signs in the first, second, third and fourth drive signal: +/+, +/−, −/+ and −/−, respectively. In addition, there is a group of diodes comprising a first, second, third and fourth diode. These diodes are coupled for transferring the first, second, third and fourth drive signal respectively, to an output. The first and fourth diodes have the same polarity relative to the output. The second and third diodes also have the same polarity relative to the output, but opposite to that of the first and fourth diodes.
The driving circuit can be realized without utilizing a transformer. For example, the driving circuit may be realized by using only transistors, resistors and capacitors. The group of diodes can be connected to the output without the intervention of such a transformer. Thus, a mixer circuit according to the invention does not need a transformer unlike the mixer circuit according to the prior art. In consequence, a diode mixer circuit according to the invention can be used in applications for which the mixer circuit according to the prior art is not suitable because of the fact that it contains transformers. Thus, the invention makes a larger variety of applications possible.
More particularly, a diode mixer according to the invention can be realized in the form of an integrated circuit, whereas this is practically impossible for the prior-art circuit. Certain applications require that a mixer circuit is realized in the form of an integrated circuit, for example, for reasons of cost and/or dimensions. Thus the invention allows the use of a diode mixer circuit in such an application.
Another advantage of the invention is the following. A diode mixer circuit is capable of reaching a relatively favorable performance, notably in terms of noise and distortion. As explained above, the invention allows the use of a diode mixer circuit in an application for which the mixer circuit according to the prior-art is unsuitable. Thus, the invention allows such an application to benefit from favorable performance of a mixer circuit included therein.
The invention may advantageously be applied in a receiver. In general, the frequency of an input signal of a receiver is converted by mixing it with a signal coming from an oscillator. The invention permits this frequency conversion to be realized with a diode mixer circuit even in the case where the receiver is to be relatively inexpensive and/or relatively small. It has already been mentioned that a diode mixer circuit is capable of reaching a low noise level and a low distortion level. Thus, the invention makes it possible to carry out the frequency conversion without affecting the input signal too much. In general, the processing of the input signal as regards frequency conversion influences the performance of the receiver to a large extent. Consequently, the invention may considerably contribute to a satisfactory performance level of the receiver.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
REFERENCES:
patent: 3983489 (1976-09-01), Gittinger
patent: 4355420 (1982-10-01), Ishihara
patent: 6118992 (2000-09-01), Watanabe
By James K. Hardy, “High-Frequency Circuit Design” Preston Publishing Company, 1979, pages 318.
Baltus Petrus G. M.
Stikvoort Eduard F.
Tombeur Antoon M. H.
Aoki Makoto
Eisenzopf Reinhard
Halajian Dicran
U.S. Philips Corporation
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