Wave transmission lines and networks – Frequency multipliers
Reexamination Certificate
2001-01-12
2002-04-09
Lam, Tuan T. (Department: 2816)
Wave transmission lines and networks
Frequency multipliers
C327S119000, C327S122000, C327S123000
Reexamination Certificate
active
06369675
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a frequency multiplier to be used as a high-stability, low-noise signal source for microwave and millimeter-wave communication systems.
As a constitution of the high-stability, low-noise signal source for microwave and millimeter-wave communication systems, there has been provided a technique that with a plurality of frequency multipliers connected in series on the output side of a PLL (phase-locked loop) oscillator that generates low frequency signals, an output frequency of the PLL oscillator is sequentially multiplied to obtain a signal of a desired frequency. In such a PLL oscillator, conventionally, it has been common practice to connect in series frequency multipliers that doubles the frequency.
An example of the frequency multiplier as a doubler is shown in “Monolithic Microwave Integrated Circuits (edited by the Institute of Electronics, Information and Communication Engineers), pp. 125-127”. This frequency multiplier, as shown in
FIG. 7
, comprises an input-side matching circuit
101
, an FET (Field Effect Transistor)
102
, a transmission line
103
, an end-open stub
104
, and an output-side matching circuit
105
.
In the frequency multiplier of this constitution, with the gate of the FET
102
biased to around the pinch-off, a large-amplitude input signal with frequency f
0
is inputted to the gate of the FET
102
via the matching circuit
101
. Then, the drain waveform of the FET
102
becomes close to a half-wave rectified one, which has a large portion of frequency components that are integral multiples of the input signal frequency f
0
, particularly even-ordered frequency components. On the drain side of the FET
102
, a fundamental-wave trap circuit employing the end-open stub
104
is used to suppress the fundamental wave. Because the length of the end-open stub
104
is selected so as to be an electrical length of 90° with respect to the fundamental wave of the input signal, the connecting point of the end-open stub
104
is short-circuited to the input signal fundamental wave and appears open to the doubled wave, so that fundamental-wave components are suppressed and the doubled wave is outputted. This frequency multiplier has an additional amplification effect by the FET
102
so that a high-efficiency frequency multiplication can be achieved.
Also, an example of frequency multipliers that quadruple the frequency at one stage with a view to reduction in the number of stages to be connected is shown in “A {fraction (15/60)} ONE-STAGE MMIC FREQUENCY QUADRUPLER”, IEEE, 1996 Microwave and Millimeter-Wave Monolithic Circuits Symposium pp. 35-38”.
This frequency multiplier as a quadrupler, as shown in
FIG. 8
, comprises an input-side matching circuit
201
, a transmission line
202
, an end-open stub
203
having an electrical length of 90° with respect to the doubled wave, an end-open stub
204
having an electrical length of 90° with respect to the quadrupled wave, an HEMT (High Electron Mobility Transistor)
205
, a transmission line
206
, an end-open stub
207
having an electrical length of 90° with respect to the doubled wave, an end-open stub
208
having an electrical length of 90° with respect to the fundamental wave, and an output-side matching circuit
209
. Because the end-open stub
208
having an electrical length of 90° with respect to the fundamental wave and the end-open stub
207
having an electrical length of 90° with respect to the doubled wave are connected to the circuit on the drain side of the HEMT
205
, there appears no signals of the fundamental wave (frequency f
0
) and the doubled wave (frequency
2
f
0
). These end-open stubs are open to the signal of the quadrupled wave (frequency
4
f
0
), so that the signal of the quadrupled wave is outputted. Also, because the end-open stub
203
having an electrical length of 90° with respect to the doubled wave and the end-open stub
204
having an electrical length of 90° with respect to the quadrupled wave are connected to the input side, signals of the doubled wave (frequency
2
f
0
) and the quadrupled wave (frequency
4
f
0
) reflected from the HEMT
205
toward the input side are suppressed.
With regard to the frequency multiplier as a doubler, when frequency multipliers are connected in series in multiple stages to obtain a desired frequency, the number of high-frequency transistors (FETs) increases with increasing number of order of frequency multiplication. This causes problems of increased complexity of the circuit and increased power consumption.
Also, in frequency multipliers as doublers and frequency multipliers as quadruplers, at voltages higher than the pinch-off, the drain current of the FETs (including HEMTs) generally exhibits a square characteristic to the gate voltage. This causes a problem of poor efficiency at the time when harmonics of tripled wave or higher-ordered waves are taken out.
Therefore, an object of the present invention is to provide a frequency multiplier which is capable of taking out fourth- or higher-ordered harmonics efficiently with a simple constitution using one high frequency transistor, and which can be reduced in size and stabilized in operation.
In order to achieve the aforementioned object, there is provided a frequency multiplier comprising:
an input-side matching circuit;
a high frequency transistor with base or gate connected to an output terminal of the input-side matching circuit and with emitter or source grounded;
first signal transmission means with one end connected to collector or drain of the high frequency transistor;
doubled-wave reflection means with one end connected to the other end of the first signal transmission means;
second signal transmission means with one end connected to the other end of the first signal transmission means;
fundamental-wave reflection means with one end connected to the other end of the second signal transmission means; and
an output-side matching circuit with its input terminal connected to the other end of the second signal transmission means.
In an embodiment of the present invention, the first signal transmission means is a first transmission line;
the second signal transmission means is a second transmission line;
the doubled-wave reflection means is an end-open stub for blocking passage of a doubled wave; and
the fundamental-wave reflection means is an end-open stub for blocking passage of a fundamental wave.
According to this frequency multiplier, when an input signal is inputted to the base of the high frequency transistor (e.g., bipolar transistor) via the input-side matching circuit, the collector current of the high frequency transistor increases exponentially relative to the base voltage, so that many harmonics are outputted. Then, because a short-circuit to the fundamental wave is formed at the connecting point of the end-open stub for blocking the passage of the fundamental wave, the fundamental wave is reflected toward the high frequency transistor. Also, because a short-circuit to the doubled wave is formed at the connecting point of the end-open stub for blocking the passage of the doubled wave, the doubled wave is reflected toward the high frequency transistor. Thus, only harmonics of quadrupled wave or higher-ordered waves are outputted via the output-side matching circuit. When this occurs, the fundamental wave is reflected toward the high frequency transistor by the end-open stub for blocking the passage of the fundamental wave, so that the output power of the doubled wave is increased by the multiplying effect of the high frequency transistor. The doubled wave of increased output power is further reflected toward the high frequency transistor by the end-open stub for blocking the passage of the doubled wave, so that the output power of the quadrupled wave is further increased by the multiplying effect of the high frequency transistor. Also, in order that the fundamental wave is converted to the doubled wave to a maximum while the doubled wave is converted to the quadrupled wave to a maximum, the electrical lengths of
Lam Tuan T.
Sharp Kabushiki Kaisha
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