Oscillators – Combined with particular output coupling network
Reexamination Certificate
1999-01-27
2001-06-26
Kinkead, Arnold (Department: 2817)
Oscillators
Combined with particular output coupling network
C331S025000, C331S096000, C455S073000, C455S076000, C455S264000, C455S315000
Reexamination Certificate
active
06252468
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a signal generator using a voltage-controlled oscillator (VCO), and more particularly to a signal generator for generating one input signal of a frequency mixing circuit (MIX).
2. Related art
A VCO which is capable of controlling an oscillation frequency by means of voltage is used as a local oscillating source of a receiving system or an intermediate frequency signal source of a transmitting system. The VCO is not used as a single unit but is used by being incorporated as a part of a phase-locked loop (PLL). As for the VCO which is used as the intermediate frequency signal source of the transmitting system, its oscillation frequency is modulated by a modulating signal. Phase-shift keying (FSK) is one desirable system of modulation. In a communication apparatus which combines transmitting and receiving functions, one VCO is used jointly for the transmitting system and the receiving system.
FIG. 4
is a block diagram illustrating a schematic configuration of a frequency conversion portion of a communication apparatus of this type. In this drawing,
1
T denotes a transmitting mixer (frequency mixing circuit), and
1
R denotes a receiving mixer.
First input signals of these mixers
1
T and
1
R are both supplied from a VCO
2
. A second input signal of the transmitting mixer
1
T is an internal local oscillation signal of a fixed frequency. A second input signal of the receiving mixer
1
R is a high frequency.
Each of the mixers
1
T and
1
R outputs a beat signal having a frequency corresponding to the difference or sum of two input signals. An output of the transmitting mixer
1
T becomes a transmitting RF signal, while an output of the receiving mixer
1
R becomes an intermediate frequency (IF) signal. In a case where the frequency of a received RF signal is high, the output of the receiving mixer
1
R becomes a first IF signal.
The VCO
2
is built in a closed loop including a PLL circuit
3
and a loop filter circuit
4
, and the oscillation frequency is stabilized. In general, a circuit block including the VCO
2
, the PLL circuit
3
, and the loop filter
4
is contained in a signal generator called a PLL module
5
in one chip. In the example of
FIG. 4
, a crystal oscillator which is externally connected to the PLL circuit
3
and an external circuit for inputting a modulating signal for transmission to the VCO
2
are omitted in the drawing.
As shown in
FIG. 4
, in the configuration of the apparatus in which an output terminal of the conventional PLL module
5
in which the VCO
2
is disposed in an output stage is directly coupled to the input sides of the mixers
1
T and
1
R, the impedance in a stage following the mixers
1
T and
1
R is liable to be affected by the output impedance of the VCO
2
and a change in the oscillation frequency.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a signal generator which overcomes the above-described problem, and in which the impedance subsequent to mixers need not be changed even if an output terminal of the signal generator is directly coupled to the mixers for which an output of a VCO is set as one input signal.
The above object of the present invention can be attained by a signal generator which imparts one of two input signals to a frequency mixing circuit which mixes two input signals and outputs a signal having a frequency which is a difference between frequencies of the two signals or a sum thereof, comprising: a voltage-controlled oscillator for generating one of the input signals; an attenuating circuit for attenuating an output signal of the voltage-controlled oscillator; and a filter circuit for limiting a frequency band of an output signal from the attenuating circuit.
In accordance with an embodiment of the present invention, the voltage-controlled oscillator is used jointly for a frequency mixing circuit for transmission and a frequency mixing circuit for reception of an FSK transmitting/receiving apparatus, for example. As a more specific configuration, the voltage-controlled oscillator is incorporated as a part of a phase-locked loop, and the attenuating circuit and the filter circuit are built in a PLL module in which the phase-locked loop including the voltage-controlled oscillator is formed as one chip.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1
is a block diagram illustrating an embodiment of a signal generator in accordance with the present invention;
FIG. 2
is a circuit diagram illustrating the details of essential portions of
FIG. 1
;
FIG. 3
is a block diagram illustrating a specific example in which the present invention is applied to an FSK transmitting/receiving apparatus; and
FIG. 4
is a block diagram illustrating one example of a conventional frequency converter.
REFERENCES:
patent: 3310746 (1967-03-01), Ward
patent: 5598405 (1997-01-01), Hirose
patent: 5794131 (1998-08-01), Cairns
patent: 5878332 (1999-03-01), Wang et al.
RF Design Guide: Systems, Circuits, and Equations pp. 64, 164 & 165 by Peter Vizmuller, 1995.
Kinkead Arnold
McGuireWoods LLP
Mitsumi Electric Co. Ltd.
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