Pulse or digital communications – Receivers
Reexamination Certificate
1999-12-08
2001-10-23
Tse, Young T. (Department: 2634)
Pulse or digital communications
Receivers
C375S350000
Reexamination Certificate
active
06307897
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radio receiving apparatus used in mobile communications equipment, and more particularly to a radio receiving apparatus which can reduce the number of high-frequency circuit parts, and hence can reduce factors of high power consumption and factors causing unstable operation which factors are present in high-frequency circuits.
The invention also relates to communications equipment which transmits information while changing the bandwidth in accordance with its type, and more particularly it is intended to implement, in a simple configuration, a radio receiving apparatus for receiving communication signals of different bandwidths.
2. Description of the Related Art
One of the important points of a radio receiving apparatus in mobile communications equipment is how to reduce the number of high-frequency circuit parts to reduce factors of high power consumption and factors causing unstable operation, which are present in high-frequency circuits, thereby reducing the manufacturing cost and a space occupied by the high-frequency circuit parts. One of the causes for the fact that the high-frequency parts of the radio receiving apparatus are made complex is that it is very difficult to realize a sharply-attenuating channel filter for separating a desired channel band from its adjacent channels, and a desired filtering characteristic needs to be established step by step.
An example of the configuration of a radio receiving scheme used in current mobile communications equipment is shown in FIG.
38
. In addition, as another conventional example,
FIG. 39
shows a direct demodulation scheme in which the local oscillation frequency is set at a carrier frequency, i.e., a direct-conversion receiving scheme for direct conversion into a baseband (Japanese Unexamined Patent Publication No. Hei. 6-164243).
In
FIG. 38
, a radio signal having a frequency fc enters an antenna ANT, and is amplified by a low-noise amplifier LNA. The amplified radio signal is passed through a bandpass filter BPF
1
to separate overall subject frequency channels of the communications system from other communication signal groups. Its output is converted into a first intermediate frequency by a frequency converter MIX
1
, and signal components other than the desired frequency channel are eliminated by a first intermediate frequency filter IF
1
-FLT as much as possible. Its output is amplified by a first intermediate frequency amplifier IF
1
-AMP, and is then supplied to a frequency converter MIX
2
.
As for the received signal which has been converted into a second intermediate frequency, signal components other than the desired frequency channel are further eliminated by a second intermediate frequency amplifier IF
2
-FLT. Its output is amplified by a second intermediate frequency amplifier IF
2
-AMP, and is then inputted to a quadrature wave detector Q-DET.
Here, the received signal is subjected also to frequency conversion with a second intermediate frequency fL
0
, into the baseband. The received signal is passed through a lowpass filter LPF to eliminate the signal components other than the frequency channel and to eliminate image signals in frequency conversion. Thus the desired channel signal is extracted, and is amplified to a predetermined signal strength by a baseband amplifier BF-AMP, thereby providing a reception output.
Accordingly, a description will be first given of problems encountered in the radio receiving apparatus of communications equipment which is used in the vicinity of a microwave band and which is shown in
FIG. 38
illustrating a conventional example.
As a first problem, as seen in the conventional example in
FIG. 38
, frequency conversion in three stages is carried out including quadrature detection, and filtering in four stages and amplification in four stages are effected. Three local oscillators of L
01
, L
02
, and fL
0
are needed. Therefore, the radio receiving apparatus requires numerous parts.
A second problem is that these numerous parts result in large power consumption.
Next, a consideration will be made of the example of
FIG. 39
, i.e., the direct-conversion receiving apparatus in which an attempt is made to simplify the radio receiving apparatus. In
FIG. 39
, a received AM high-frequency signal is inputted to a pair of mixers
18
and
19
and mixed with respective high-frequency signals whose frequency is equal to the carrier frequency and phases are different from each other by 90°.
Outputs of the mixers
18
and
19
are respectively inputted to phase shifters
27
and
28
via lowpass filters
23
and
24
and A/D converters
25
and
26
. The respective signals whose phases are delayed in such a manner as to be mutually different by 90° by the phase shifters
27
and
28
are inputted to a matrix circuit
29
where signals representing the sum of and the difference between the respective signals are derived.
The signals from the matrix circuit
29
are converted to analog signals by D/A converters
30
and
31
, modulated signals in both sidebands of the AM high-frequency signal are separated, and a signal with less noise is selectively outputted to a speaker
35
. A direct-conversion receiving apparatus which has less noise and radio interference is realized.
Consideration will be given to the power consumption of the circuits and the performance required of the parts in this conventional example. In the conventional example of
FIG. 39
, the channel filter for separating and extracting the received signal from adjacent interfering signals is implemented by the lowpass filters
23
and
24
and digital filters provided in digital circuits after A/D conversion.
Where signal processing is carried out by digital circuits in a demodulation circuit
42
, it is possible to simplify the filters
23
and
24
for the radio system. However, in order to obtain sufficient amplitude-separating capabilities and frequency-separating capabilities, the calculation clock rate must be sufficiently higher than the highest frequency component of the analog signal. Hence, since the operating speed of the operating portion becomes high and the operating amplitude in the digital system
42
is fixed and large at several volts, there is a drawback in that this results in an increase in power consumption which is several times greater than in a case where processing is effected by an analog system.
Further, many processing systems operate in parallel in logical circuits. That is, even if the calculation clock rate is close to a baseband frequency, the total power consumption of the circuitry becomes (square of the voltage amplitude)×(processing speed)×(electrostatic capacitance of the circuit system load)×(number of parallels), so that the total power consumption becomes large. Namely, the fact that the signal is processed by a digital circuit has a negative factor for increasing the power consumption.
As a third problem, in a case where an attempt is made to digitize the signal processing, there results an increase in power consumption which is several times greater than in a case where processing is effected by a radio system.
As a fourth problem, conventional digital filters involve complicated calculations, and require the four rules of arithmetic even when their configurations are simple, so that power consumption is not negligible.
In addition, if consideration is given to the A/D converters
25
and
26
for digitizing the signal, the voltage amplitude required of the input signal is generally large at one volt or two volts. Accordingly, in the conventional example shown in
FIG. 39
, the abilities to supply the amplitude are required of the mixers
18
and
19
in the preceding stage. It may be said that this is possible in frequencies of AM radio bands, i.e., medium-wave broadcasting bands, which are handled by the conventional example of
FIG. 39
; however, in higher frequency bands such as those for TV broadcasting and cellular phone systems, no mixers are available which are ca
Inogai Kazunori
Ohta Gen-ichiro
Sasaki Fujio
Sudo Hiroaki
Matsushita Electric Industiral Co., Ltd.
Pearne & Gordon LLP
Tse Young T.
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