Oscillators – Automatic frequency stabilization using a phase or frequency... – Tuning compensation
Patent
1995-08-11
1996-10-22
Mis, David
Oscillators
Automatic frequency stabilization using a phase or frequency...
Tuning compensation
331 8, 331 77, 327105, 327156, 455 76, 455260, 455290, 455319, H03L 708, H03L 718
Patent
active
055680984
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a frequency synthesizer, used in for example an oscillator of a transmitting system and a local oscillator within a frequency converter circuit of a receiving system in a radio communication device, for multiplying and supplying an oscillated signal which has been stabilized in frequency by a PLL (phase locked loop) to such transmitting and receiving systems.
BACKGROUND ART
Conventionally, a frequency synthesizer of this kind is formed of a PLL comprising an oscillator using a quartz-crystal oscillator, a phase comparator, a divider (programmable one), a VCO (voltage controlled oscillator), etc. Such a frequency synthesizer generates and outputs an oscillation signal of a frequency variable by constant spacings by locking the VCO on the basis of the phase difference between a reference oscillation signal from the oscillator and the output oscillation signal and using the divider.
FIG. 1 is a block diagram showing an arrangement of a radio transmitter using a prior art frequency synthesizer. In FIG. 1, the radio transmitter comprises a frequency synthesizer 1 for supplying an stable output oscillation signal SA with a frequency variable by constant spacings, a quadrature modulator 2 for applying QPSK (quadrature phase shift keying) or QAM (quadrature amplitude modulation) to the output oscillation signal SA by using phase angle modulation signals (I and Q signals), a power amplifier 3 for amplifying the modulated high frequency signal SM from the quadrature modulator 2 for transmission, and an antenna 4 for radiating the high frequency electric power SP from the power amplifier 3 as radio wave. Also, the frequency synthesizer 1 is provided with a reference signal oscillator 5 for oscillating a reference signal, and a phase comparator 6 for making a phase comparison between a frequency-divided signal and the reference oscillation signal from the reference signal oscillator 5. And, it is also provided with a low pass filter (LPF) 7 for removing undesirable harmonics and noise from a phase error signal from the phase comparator 6 and supplying a DC voltage, a voltage controlled oscillator (VCO) 8 for sending out an output oscillation signal SA with its frequency locked by the DC voltage from the LPF 7, and a frequency divider 9 for frequency-dividing the output oscillation signal so as to provide a frequency-divided signal which is frequency-variable by constant spacings and for supplying the frequency-divided signal to the phase comparator 6.
Here, we discuss operation of the radio transmitter or a prior art example, in the following.
The phase comparator 6 in the frequency synthesizer 1 compares the phases of the reference oscillation signal from the reference signal oscillator 5 and the frequency-divided signal from the frequency divider 9. The phase error signal obtained from the comparison is passed through an LPF 7, which removes undesirable harmonics and noise from the phase error signal from the phase comparator 6 to yield a DC voltage, that is, a frequency controlling signal, which is applied to the control terminal of a VCO 8. It is noted that the amplitude and phase characteristics of the LPF 7 determines the response and synchronization characteristics of the PLL in this frequency synthesizer 1. That is, selecting the inductance and capacitance of the LPF is to set a time characteristic of the frequency divider 9 with respect to frequency shift. The frequency synthesizer 1 supplies a stable output oscillation signal SA with a frequency variable by constant spacings to the quadrature modulator 2, which applies modulation such as (QPSK and (QAM with phase angle modulation signals (I and Q signals) to the output oscillation signal SA for output. The modulated radio signal SM is power amplified by the power amplifier 3 to radiate the amplified radio signal power SP through the antenna 4 as radio wave.
In such transmitter, the radio signal power SP from the power amplifier 3 is relatively large. For this reason, in order to prevent undesirable radiation leaki
REFERENCES:
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patent: 3921056 (1975-11-01), Mahoney
patent: 4039968 (1977-08-01), Emshwiller
patent: 4176332 (1979-11-01), Bachert
patent: 4231116 (1980-10-01), Sekiguchi et al.
Horie Hiroshi
Tobita Tsutomu
Mis David
Toshiba Corporation
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