Pulse or digital communications – Synchronizers – Phase displacement – slip or jitter correction
Reexamination Certificate
1998-03-04
2001-02-13
Vo, Don N. (Department: 2734)
Pulse or digital communications
Synchronizers
Phase displacement, slip or jitter correction
Reexamination Certificate
active
06188740
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a fractional-N system frequency synthesizing method and a fractional-N system frequency synthesizer which can suppress spurious components in the vicinity of an oscillation frequency, and a field pickup unit which can selectively provide a plurality of different channel frequencies for use in digital data transmission and which uses the frequency synthesizer.
DESCRIPTION OF THE RELATED ART
As well known, for example, in television broadcasting, a video signal picked up by a television camera and a voice signal obtained by a microphone are used. In relaying of television broadcasting to a television broadcasting station from the outside, a video/voice signal is required to be transmitted from a relaying point outside the television broadcasting station to the station. To this end, a broadcasting field pickup unit (FPU) is used as the case may be.
Conventionally, a video/voice signal picked-up/collected as an analog signal is transmitted as it is, namely, in an analog signal form. Precently, however, with advancement of digital techniques, the analog video/voice signal is converted to a corresponding digital video/voice signal, which is then transmitted.
Usually, a ground television broadcasting station is authorized to use a radio frequency band assigned for its broadcasting enterprise. A single television broadcasting station is allocated a plurality of different channels (frequency bands) for use in an FPU. Each frequency band width is, for example, about 700 MHz in a 7 GHz band and about 500 MHz in a 10 GHz band.
Thus, there are known FPUs which are each composed of a pair of transmitter and receiver wherein its PLL frequency synthesizer controls a VCO in correspondence to a plurality of channels to thereby select a desired channel.
A conventional FPU which uses a PLL frequency synthesizer to perform analog signal transmission (frequency modulation) will be described next with respect to FIG.
4
. The FPU is composed mainly of a transmitter
50
and a receiver
60
.
The transmitter
50
is composed of a transmission control unit
51
which receives a video/voice signal to be transmitted and produces an intermediate frequency (IF) signal by frequency-modulating a carrier wave of a predetermined frequency with the received signal; a transmission high-frequency unit
53
which converts the frequency of the IF signal received via a coaxial cable
52
from the transmission control unit
51
and amplifies the power of a transmission signal; a transmission antenna
54
connected to the transmission high-frequency unit
53
for transmitting a power-amplified microwave signal. The transmission high-frequency unit
53
is composed of a TX converter
55
which amplifies the IF signal received via the cable
52
and converts its frequency; a local oscillator
56
; a voltage controlled oscillator (VCO)
57
; a PLL frequency synthesizer
58
; and a power amplifier
59
.
The receiver
60
is composed of a receiving antenna
64
which receives the microwave signal transmitted by the transmitter
50
; a reception high-frequency unit
63
connected to the receiving antennal
64
for high-frequency amplifying and converting a received signal; a reception control unit
61
for demodulating an IF signal received from the reception high-frequency unit
63
via a coaxial cable
62
and outputting a video/voice signal. The reception high-frequency unit
63
is composed of a high-frequency amplifier
69
; an RX converter
65
which converts the frequency of a signal received from the high-frequency amplifier
69
to the IF signal and provides AGC control, a VCO
67
, a PLL frequency synthesizer
68
and a local oscillator
66
.
In operation, when the FPU is used, for example, for television broadcasting relaying purposes, the receiver
60
is installed within a broadcasting station concerned, whereas the transmitter
50
is set outside the television broadcasting station.
Signals, for example, a video signal picked up by a television camera and a voice signal collected by a microphone and transmitted via the FPU, are inputted to the transmission control unit
51
of the transmitter
50
.
The transmission control unit
51
includes a carrier wave oscillator for generating a carrier wave signal of a predetermined frequency and a frequency modulator (both not shown). A carrier wave signal of a predetermined frequency, for example, of 130 MHz produced and outputted by the carrier wave oscillator is frequency-modulated in the frequency modulator with an inputted video/voice signal to provide an IF signal whose carrier wave frequency is 130 MHz, which is then sent via the coaxial cable
52
to the transmission high-frequency unit
53
which converts the frequency of the IF signal and amplifies its power.
The IF signal sent to the transmission high-frequency unit
53
is inputted to the TX converter
55
of the transmission high-frequency unit
53
. The TX converter
55
converts the IF signal to a second IF signal, for example, of a carrier wave signal of 1.5 GHz. An oscillation signal of a predetermined frequency delivered by the local oscillator
56
is used as a transmission first local oscillation signal.
The TX converter
55
also converts the carrier wave frequency (1.5 GHz) of the second IF signal to a signal of a microwave band (radio wave band including 7 GHz/10 GHz radio wave) and outputs the obtained microwave and signal to the power amplifier
59
.
In this frequency conversion, an oscillation signal of a required frequency fed from the VCO
57
controlled by the PLL synthesizer
58
is used as a transmission second local oscillation signal.
The power amplifier
59
amplifies the microwave band signal fed from the TX converter
55
to a predetermined transmission power, outputs the amplified signal to the sending antenna
54
which transmits the amplified microwave band signal toward the receiver
60
.
The receiver
60
receives the microwave band signal transmitted by the transmitter
50
with the receiving antenna
64
, and feeds the received signal to the reception high-frequency unit
63
. The high-frequency amplifier
69
in the reception high-frequency unit
63
receives and amplifies the microwave band signal to a signal of a required power level and outputs the resulting signal to the RX converter
65
, which converts the frequency of the amplified microwave signal to a second IF signal whose carrier wave frequency is 1.5 GHz. In this frequency conversion, an oscillation signal outputted by the VCO
67
controlled by the PLL frequency synthesizer
68
is used as a reception first local oscillation signal.
The RX converter
65
converts the second IF signal of the carrier wave signal of 1.5 GHz to an IF signal whose carrier wave frequency is 130 MHz, which is then delivered via the coaxial cable
62
to the reception control unit
61
. In this frequency conversion, the oscillation signal fed from the local oscillator
66
is used as a reception second local oscillation signal.
The reception control unit
61
is provided with a carrier wave oscillator for generating a carrier wave signal of a predetermined frequency and a FM (frequency-modulation) demodulator (both not shown), and FM-demodulates the IF signal, whose carrier wave frequency is 130 MHz, inputted from the RX converter
65
and outputs the resulting video/voice signal to a succeeding stage device (not shown).
Another conventional FPU which transmits a digital signal will be described next with reference to FIG.
5
. At this figure, same reference numerals are used to identify similar components of FIG.
4
and further description thereof will be omitted.
In the transmitter
50
, a transmission control unit
71
receives an analog video/voice signal to be transmitted and converts the same to a corresponding digital video/voice signal, and which modulates a carrier wave of a predetermined frequency with the digital video/voice signal in accordance with a predetermined modulation system, for example, in an amplitude modulation system, to produce an intermediate frequency (I
Antonelli Terry Stout & Kraus LLP
Hitachi Denshi Kabushiki Kaisha
Vo Don N.
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