Pulse or digital communications – Receivers – Angle modulation
Reexamination Certificate
1999-01-25
2003-12-23
Tran, Khai (Department: 2631)
Pulse or digital communications
Receivers
Angle modulation
C455S180300
Reexamination Certificate
active
06668025
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a tuning demodulator for digitally modulated RF signals for detecting RF signals digitally modulated by television signals or the like.
A conventional tuning demodulator for digitally modulated RF signals for receiving and detecting RF signal digitally modulated by television signal or the like, for example, RF signal in 1-2 GHz band is as shown in
FIG. 11
, in which the RF signal entered from an RF signal input terminal
301
through a receiving antenna is amplified in an RF circuit
302
, and enters a mixing circuit
303
, and is mixed with an output signal of a local oscillation circuit
304
of which output frequency is in a same RF band as the RF signal, for changing the output frequency while keeping a specific frequency difference from the frequency of a desired receiving channel, and the station is selected by converting the frequency of the desired receiving channel to an IF signal, for example, a signal in 400 MHz band. Moreover, this IF signal is amplified in an IF circuit
306
(IF amplification), and passed through a band pass filter (IF BPF), and then it is put into an I/Q detection circuit
306
together with an output signal of a detection oscillator
307
of which output frequency is in IF band, and undergoes orthogonal demodulation (or quadrature demodulation) to be taken out from output terminals
308
a
, and
308
b
as so-called I signal and Q signal. (In this specification, I and Q signals are not color difference signals as defined in the NTSC system, but are modulation signals which modulate carriers differing in phase by 90°.) In this conventional apparatus, since the RF is once converted into an IF signal (hereinafter called down-converting method), if the oscillation signal of the local oscillation circuit
304
leaks from the RF input terminal
901
, its frequency is apart from the RF signal by the portion of the IF frequency, and it has no interference on other receiving apparatus having the same receiving frequency band, but as known from
FIG. 11
, the mixing circuit and oscillation circuit are required by two pieces each, such as
303
,
306
, and
304
,
307
, and the tuning demodulator for digitally modulated RF signals itself is complicated, and there are problems in design and manufacture. It was accordingly proposed to simplify and downsize the apparatus by selecting the station and detecting simultaneously (hereinafter called direct detection method) by using an oscillation circuit for detection, without employing the down-converting method, of which output frequency is nearly same as the frequency of the desired receiving channel in the RF signal, but in this method, the problem was that the oscillation signal of the oscillation circuit for detection leaks from the RF input terminal to impede other receiving apparatus having the same receiving frequency band, and any prior art overcoming this problem was not known yet.
Incidentally, the output signal in the local oscillation circuit of down-converting method or oscillation circuit for detection in direct detection method in the case of receiving 12 GHz band satellite broadcast by using a consumer receiving system is generated accurately and stably by a PLL frequency synthesizer on the basis of the nominal frequency of broadcast, but in the 12 GHz band receiving antenna, since the frequency is not converted accurately and stably into 1-2 GHz band as in the PLL frequency synthesizer, the frequency of the RF input signal is slightly deviated usually from the nominal frequency to cause a frequency error.
FIG. 12
shows a tuning demodulator far digitally modulated RF signals having a function of compensating for the frequency error by the direct detection method, which corresponds to the QPSK modulated RF signals. In this conventional apparatus, the output frequency (that is, the frequency of output signal) of an oscillation circuit for detection
404
is set by a PLL frequency synthesizer
404
a
so as to coincide with the nominal frequency of the input signal to be selected on the basis of the output frequency of a reference oscillator
408
, but actually it remains fixed even if the RF signal has a frequency error, and there was a possibility of deterioration of bit error rate in a later stage. The output of the detection circuit
404
is put into A/D converters
409
a
and
409
b
through low pass filters
408
a
and
400
b
, and is converted into a digital signal by using a clock signal regenerated in a clock regenerating circuit
412
. Afterwards, in a first complex multiplier
411
, the frequency error is compensated by using the output signal of a frequency error detection circuit
414
, and therefore deterioration of bit error rate is prevented. Further later, in order to avoid interference between signals, a clock signal and a carrier signal are regenerated in a second complex multiplier
416
, together with the clock regeneration circuit
412
and carrier regeneration circuit
413
, through roll-off filters
410
a
and
410
b
, while data is detected from its output signal in a data detection circuit
417
, and clock signal and data signal are issued from output terminals
418
a
and
418
b
, respectively. Incidentally, all circuits enclosed by broken line
420
in
FIG. 12
are integrated into an one-chip LSI. Such conventional apparatus, however, requires a circuit to compensate for frequency error, such as the complex multiplier
411
, and the apparatus itself is complicated to cause problems in design and manufacture, and moreover in order to compensate for the frequency error by the complex multiplier
411
only, its operation bit number must be sufficiently large, which causes to deteriorate the bit error rate.
Thus, the conventional tuning demodulators for digitally modulated RF signals, whether in down-converting method or in direct detection method, were complicated in apparatus, increased in size, and raised in coat, and had problems in performance such as leek of interference radio wave and deterioration of bit error rate. The tuning demodulator for digitally modulated RF signals of the invention is not only simplified in apparatus, reduced in size, and lowered in cost, but also presents various benefits to contribute to reduction of leak of interference radio wave, improvement of bit error rate, and enhancement of station selection performance.
SUMMARY OF THE INVENTION
To solve the above problems, it is a first object of the invention to present a tuning demodulator for digitally modulated RF signals simplified in apparatus, reduced in size, and lowered in cost, by facilitating the means for suppressing leakage of oscillation signal of the oscillation circuit for detection from the RF input terminal, in the tuning demodulator for digitally modulated RF signals by direct detection method for selecting and detecting digitally modulated RF signals simultaneously, and it is a second object to present a tuning demodulator for digitally modulated RF signals simplified in apparatus, reduced in size, and lowered in cost, as well as improved in the bit error rate and enhanced in the station selecting performance, without requiring the hitherto needed complex multiplier for compensation of frequency error.
To achieve the first object, the invention is characterized by generating an unmodulated wave having a frequency nearly equal to the frequency of desired reception signal among RF signals digitally modulated to be put in an RF input signal, in an oscillation circuit for detection, selecting a station and detecting simultaneously by entering this output signal and the RF signal amplified through the input terminal and RF circuit into an I/Q detection circuit, issuing detected I and Q original signals, and suppressing leak of the oscillation signal of the oscillation circuit into the input terminal by radiation into path other than the intended signal path, that is, into the space, by disposing physical and/or electrical signal separating means between the RF circuit and the oscillation circuit (hereinafter, in the inv
Adachi Kenji
Sumi Shigeharu
Matsushita Electric - Industrial Co., Ltd.
RatnerPrestia
Tran Khai
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