Pulse or digital communications – Receivers – Interference or noise reduction
Reexamination Certificate
1999-01-08
2001-08-28
Chin, Stephen (Department: 2734)
Pulse or digital communications
Receivers
Interference or noise reduction
C455S307000
Reexamination Certificate
active
06282252
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a receiver suitable for data transmission, which transmits data through the use of a satellite broadcasting system.
2. Description of the Related Art
A conventional receiver for data transmission (hereinafter called simply “a receiver”) will be explained in accordance with FIG.
2
.
FIG. 2
shows a part of a circuit for the conventional receiver.
A data transmission signal is first transmitted from a satellite in a 11 GHz to 12 GHz band corresponding to the same frequency band as that for satellite broadcasting signals. The data transmission signal is frequency-converted to a band of about 950 MHz to 2150 MHz by an unillustrated down converter provided outdoors, after which it is inputted to an input terminal
31
of the receiver.
The data transmission signal (hereinafter called “received signal”) inputted to the input terminal
31
is amplified by a low-noise amplifier
32
after which it is inputted to a mixer
34
through a first variable attenuator
33
. An unillustrated PIN diode is used for the first variable attenuator
33
. The amount of attenuation thereof is controlled by a current which flows through the PIN diode. The mixer
34
is comprised of a dual gate MOS FET (Field Effect Transistor) (hereinafter called simply “FET”). The received signal is inputted to a first gate of the FET. Each local oscillation signal generated from a local oscillator
35
is inputted to a second gate of the FET through a buffer amplifier
36
. The mixer
34
frequency-converts the received signal to an intermediate frequency signal whose center frequency is about 480 MHz. Thus, the local oscillator
35
generates oscillations between about 1430 MHz and 2630 MHz in association with a frequency band for the received signal.
The intermediate frequency signal is outputted from the drain of the FET for the mixer
34
and inputted to a second variable attenuator
38
through an impedance matching circuit
37
. The impedance matching circuit
37
is used to match the output impedance of the FET corresponding to the mixer
34
to the impedance of the second variable attenuator
38
and comprises a capacitor
37
a
, an inductor
37
b
and a resistor
37
c
electrically connected in parallel. A PIN diode is used even for the second variable attenuator
38
although not shown in the drawing. The amount of attenuation thereof is controlled by a current which flows through the PIN diode.
The intermediate frequency signal whose level is controlled by the second variable attenuator
38
, is inputted to a demodulator
42
via a first intermediate frequency amplifier
39
, an intermediate frequency filter
40
and a second intermediate frequency amplifier
41
in that order. The intermediate frequency filter
40
is made up of a bandpass filter whose center frequency is about 480 MHz and whose bandwidth is about 30 MHz. Further, the intermediate frequency signal is demodulated by the demodulator
42
from which baseband signals (I signal and Q signal) are outputted.
On the other hand, the output of the second intermediate frequency amplifier
41
is inputted even to a detector
43
. The detector
43
detects it and outputs an AGC voltage therefrom. The output AGC voltage is suitably amplified by a DC amplifier
44
, followed by supply to the first variable attenuator
33
and the second variable attenuator
38
, whereby the currents flowing through their PIN diodes are controlled.
That is, the amount of attenuation of the first variable attenuator
33
and the amount of attenuation of the second variable attenuator
38
are controlled according to the AGC voltage obtained based on the output of the second intermediate frequency amplifier
41
, whereby the level of the received signal corresponding to the RF signal inputted to the mixer
34
and the level of the intermediate frequency signal inputted to the demodulator
42
are controlled so as to become approximately constant respectively.
In the conventional receiver described above, the first variable attenuator
33
and the second variable attenuator
38
are provided on the input and output sides of the mixer
34
respectively to control the level of the RF signal inputted to the mixer
34
and the level of the intermediate frequency signal inputted to the demodulator
42
so that they are held constant. Since, however, the PIN diodes are respectively used for the first variable attenuator
33
and the second variable attenuator
38
, they are excited by the RF signal and the intermediate frequency signal respectively. As a result, large white noise is produced because the PIN diode used for the second variable attenuator
38
is particularly excited by the intermediate frequency signal whose level is made high by conversion gain of the mixer
34
. In doing so, the white noise enters into the local oscillator
35
side through terminal-to-terminal capacitance between the second gate and drain of the FET constituting the mixer
34
, so that a C/N ratio between the local oscillation signals is deteriorated.
That is, since a terminal-to-terminal capacitance of about 0.05 pF exists between the drain and second gate of the FET and a series resonance circuit having a resonance frequency of about 1800 MHz is formed between the terminal-to-terminal capacitance and the inductor
37
b
constituting the impedance matching circuit
37
, a frequency component close to the resonance frequency, of the white noise produced from the PIN diode for the second variable attenuator
38
enters the local oscillator
35
to deteriorate the C/N ratio between the local oscillation signals.
Thus, since the received signal inputted to the mixer
34
is frequency-converted to the intermediate frequency signal, based on the local oscillation signals poor in C/N ratio, phase noise is superimposed on the frequency-converted intermediate frequency signal. Therefore, a problem arises in that so-called bit errors occur in data extracted based on I and Q signals corresponding to the baseband signals outputted from the demodulator
42
. Its bit-error rate tends to increase as the amount of transmission of data decreases. This is because the ratio of noise to the number of data is considered to increase.
SUMMARY OF THE INVENTION
With the foregoing in view, it is therefore an object of the present invention to provide a receiver for data transmission, which is capable of reducing bit errors caused by deterioration of a C/N ratio between local oscillation signals due to white noise produced by a variable attenuator.
According to one aspect of this invention, for achieving the above object, there is provided a receiver suitable for data transmission, comprising: a mixer for frequency-converting a received signal to an intermediate frequency signal; a local oscillator for inputting each of local oscillation signals to the mixer; a demodulator for demodulating the intermediate frequency signal to detect baseband signals; a variable attenuator provided between the mixer and the demodulator, the variable attenuator having a PIN diode so as to hold constant the level of the intermediate frequency signal inputted to the demodulator; and means for attenuating a frequency band of the local oscillation signals, the attenuating means being provided between the mixer and the variable attenuator.
In the data transmission receiver as well, the attenuating means is constructed as a band elimination filter.
Further, in the data transmission receiver, the frequency of the intermediate frequency signal is set lower than that of the local oscillation signal and the attenuating means is constructed as a low-pass filter having a cut-off frequency between the frequency of the intermediate frequency signal and that of the local oscillation signal.
Moreover, in the data transmission receiver, the frequency of the intermediate frequency signal is lower than that of the local oscillation signal and the attenuating means is made up of only a capacitor having a small capacitance value, which is electrically connected between an
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Chin Stephen
Jiang Lenny
LandOfFree
Receiver for data transmission does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Receiver for data transmission, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Receiver for data transmission will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2506453