Miscellaneous active electrical nonlinear devices – circuits – and – Specific input to output function – Combining of plural signals
Reexamination Certificate
2001-04-27
2002-09-24
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific input to output function
Combining of plural signals
C327S119000, C327S122000, C327S254000, C327S255000, C327S359000
Reexamination Certificate
active
06456143
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims benefit of priority under 35USC §119 to Japanese Patent Application No. 2000-127087 filed on Apr. 27, 2000 and Japanese Patent Application No. 2000-364648 filed on Nov. 30, 2000, the entire contents of which are incorporated by reference herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a frequency multiplier and semiconductor integrated circuit for producing a local oscillation signal for use in a superheterodyne receiver or the like.
2. Related Background Art
Recently, there are provided various systems for sending and receiving weak radio waves to carry out various processes with non-contact. For example, a keyless entry system is designed to receive weak radio waves emitted from a transmitting circuit embedded in a key for a vehicle, by a receiving circuit in the vehicle to open and close doors and so forth.
FIG. 19
is a block diagram showing schematic configuration of a conventional weak radio wave sending/receiving system of this type. The system of
FIG. 19
generally comprises a transmitter
51
and a receiver
52
. The transmitter
51
has a transmitting circuit
53
and an antenna
54
. The transmitter
51
uses a carrier frequency of 315 MHz to emit AM-modulated (amplitude-modulated) or FM-modulated (frequency-modulated) signals via the antenna
54
.
The receiver
52
comprises an antenna
11
, an SAW filter
12
, an RF amplifier
13
, a local oscillator circuit for generating a local oscillation signal, a mixer
15
for generating an intermediate frequency signal (IF signal), an IF filter
16
, an IF amplifier
17
and a detector circuit
18
. The local oscillator circuit
14
has a source oscillator circuit
21
for generating a reference signal, and a quintupler circuit
20
for outputting a quintupled signal having a frequency five times as high as that of the reference signal.
The source oscillator circuit
21
is designed to generate a source oscillation signal having a frequency of 65.14 MHz. The local oscillator circuit
14
is designed to generate a local oscillator signal f
LO
=325.7 MHz which has an increased frequency five times as high as the frequency of the source oscillation signal. The mixer
15
is designed to use the local oscillation signal f
LO
to output an intermediate frequency signal having a frequency of f
LO
−f
O
=10.7 MHz.
Thus, a high frequency signal received by the antenna
11
is converted into an intermediate frequency signal by the mixer
15
, so that the signal processing can be more easily carried out than a case of performing the signal processing by directly using the high frequency signal.
The IF filter
16
, which is a band-pass filter, is connected to the subsequent stage mixer
15
. The passing band of the filter
16
is about hundreds kHz centering on an intermediate frequency of 10.7 MHz. After undesired frequency components are removed by the IF filter
16
, the intermediate frequency signals of 10.7 MHz are amplified by about 70 dB in the IF amplifier
17
.
When the system of
FIG. 19
is applied to the above described keyless entry system, the transmitter
51
is embedded in a key carried by a human, and the receiver
52
is mounted on a vehicle. From the transmitter
51
, weak radio waves having the frequency of 322 MHz or less are emitted. An allowable field intensity is 500 &mgr;V/m or less which is defined by Article 6 of Enforcement Regulations of Radio Wave Law in Japan. Radio waves having the frequency of 322MHz or higher can be used. However, the allowable field intensity from 322 MHz to 10 GHz is 35 &mgr;V/m or less which is very small. In addition, as the frequency increases, the progressivity of radio waves increases so as not to be put to practical use, so that the radio waves having a frequency of 322 MHz or higher are hardly used in the country. Therefore, radio waves having a frequency of about 315 MHz are generally used as weak radio waves.
On the other hand, the transmitter
51
preferably has smaller electric power consumption in order to increase the life of a battery, so that it is required to simplify the circuit construction. For example, an SAW vibrator is known as a simple element capable of oscillating radio waves having a frequency of about 315 MHz. This element can not only simplify the circuit construction, but it can also directly oscillate by a frequency of 315 MHz.
Although there is a crystal oscillator as another oscillator element, it is technically difficult to directly oscillate the signal having a frequency of about 315 MHz. After oscillating the crystal oscillator at a low frequency, it is required to multiply frequency. Because of this, the SAW vibrator is often used to constitute the circuit as simple as possible.
However, there is a problem in that the SAW vibrator has a large frequency deviation. The frequency deviation of the SAW vibrator is usually 100 ppm or higher. The frequency deviation of the transmitter itself grows worse if the SAW vibrator is used as the transmitter. Because of this, when the performance and yields of products are intended to be improved, a crystal oscillator is sometimes used.
When the SAW vibrator is used as the transmitter, it is required to improve the frequency precision on the side of the receiver in order to compensate its disadvantages. In order to improve the frequency precision, a crystal oscillator having a small frequency deviation is generally used for the local oscillator circuit of the receiver. Since the frequency deviation of the crystal oscillator hardly exceeds 100 ppm at worst, it is possible to improve the frequency precision of the receiver by using the crystal oscillator for the local oscillator circuit in the receiver.
However, since it is very difficult to directly oscillate a high frequency of 300 MHz band as described above, a method for lowering the oscillation frequency of the crystal oscillator itself to multiply frequency by a frequency multiplier circuit to obtain a frequency of 300 MHz band is generally used.
There is proposed a technique using, as a conventional oscillator circuit, a quintupler circuit
20
for oscillating a crystal oscillator at 65.14 MHz to generate higher harmonics by distorting its waveform and extracting fifth-order higher harmonics by means of a filter or the like to obtain a frequency of 325.7 MHz when a local oscillation frequency of, e.g., 325.7 MHz (=315+10.7 MHz) is intended to be generated.
In this quintupler circuit
20
, it is required to increase distortion to generate higher-order higher harmonics in order to increase the multiple number. Although the level of higher harmonic components decreases as the order thereof increases, the higher harmonic components include many undesired components other than originally required fifth-order higher harmonics.
Now, assuming that a rectangular wave of an even function is used as a distorted wave and assuming that it has “1” in an interval of from (−x) to (+x) and “−1” in other intervals, the following expression can be expressed:
A
(
x−
&pgr;/2)+
A
sin x·cos &ohgr;
t+A/
2 sin 2x·cos 2
&ohgr;t+A/
3·sin 3x·cos 3
&ohgr;t+. . . +A
·sin
nx
·cos &ohgr;
t
(1)
wherein A is a constant, &ohgr; is an angular frequency which is 2&pgr;f
LO
, t is time, n is a natural number, and the first term is a dc component.
In expression (1), for example, assuming that n=5, the fifth-order higher harmonic components attenuate to ⅕ as large as a fundamental wave. Assuming that x=&pgr;/2, the odd orders of expression (1) remain, and the dc component is zero only in this case.
In order to utilize only the fifth-order higher harmonic components, first through fourth order components and sixth or higher order components must be removed. Therefore, only the fifth-order higher harmonic components are extracted by a filter using the quintupler circuit
20
. However, undesired higher harmonic components remain at a high level. The undesired higher
Imayama Teruo
Masumoto Hiroshi
Suzuki Tsuneo
Callahan Timothy P.
Luu An T.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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