Telecommunications – Receiver or analog modulated signal frequency converter – Local control of receiver operation
Reexamination Certificate
2000-03-27
2003-11-04
Trost, William (Department: 2683)
Telecommunications
Receiver or analog modulated signal frequency converter
Local control of receiver operation
C455S232100, C455S240100
Reexamination Certificate
active
06643498
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is related to a wireless receiver, a wireless receiving method, and a recording medium for recording thereon a program used to execute this wireless receiving method. More specifically, the present invention is directed to such a wireless receiver equipped with a stepped gain control type automatic gain control circuit, or a continuous gain control type automatic gain control circuit, and also directed to such wireless receiving method/recording medium used with the wireless receiver. The stepped gain control type automatic gain control circuit changes the gain only by a predetermined amount when a signal level of a reception signal exceeds a preselected level. The continuous gain control type automatic gain control circuit changes the gain in response to a signal level of a reception signal.
In presently available wireless (radio) receivers such as pagers, while automatic gain control circuits are mounted, gains of these automatic gain control circuits are controlled, so that intermodulation sensitivity suppression (will be abbreviated as an “IM” hereinafter) characteristics and over-input characteristics of these wireless receivers may be improved. Presently, there are two sorts of automatic gain control circuits. That is, in a so-called “continuous gain control type” automatic gain control circuit, a gain control amount is varied in response to a signal level of a signal entered into a wireless receiver (radio receiver). In a so-termed “stepped gain control type” automatic gain control circuit, when a signal level of a signal entered into a wireless receiver exceeds a certain constant level, a preselected amount of gain is controlled.
First, a conventional wireless receiver equipped with a continuous gain control type automatic gain control circuit will now be explained with reference to FIG.
12
and FIG.
13
.
FIG. 12
is a structural diagram for showing the conventional wireless receiver equipped with the continuous gain control type automatic gain control circuit (first prior art).
In
FIG. 12
, the wireless receiver of the first prior art is arranged by employing an antenna
501
, a low noise signal amplifier (LNA)
502
, a local oscillator circuit
503
, a frequency converting circuit
504
, a Received Signal Strength Indicator (RSSI)
505
, and a gain control circuit
506
The antenna
501
receives a signal transmitted from a base station (not shown). The low noise signal amplifier
502
amplifies the signal received by the antenna
501
. The frequency converting circuit
504
performs the signal converting operation by multiplying the signal amplified by the low noise signal amplifier
502
by the signal of the local oscillator circuit
503
. The Received Signal Strength Indicator (RSSI)
505
changes a voltage of an output signal GC
5
in response to a signal level of an intermediate frequency signal IF after being frequency-converted. The gain control circuit
506
changes a control amount of a gain in response to the output signal GC
5
outputted from the Received Signal Strength Indicator
505
.
When a level of a signal entered to the antenna
501
is changed, the signal level of the intermediate frequency signal IF which is frequency-converted by the frequency converting circuit
504
is changed in response to this signal level change. Then, the voltage of the output signal GC
5
of the Received Signal Strength Indicator
505
is varied in response to the level change of the signal IF which is frequency-converted by the frequency converting circuit
504
, so that the gain control amount of the gain control circuit
506
.
In other words, while the automatic gain control circuit is operated, when the signal level of the signal entered into the antenna
501
is high (namely, when electric field strength is strong), the gain control amount is increased, whereas when the signal level thereof is low (namely, when electric field strength is weak), the gain control amount is decreased. As previously explained, since the gain control amount will be changed in response to the signal level, the signal level of the intermediate frequency signal IF after being frequency-converted may be kept substantially constant until the gain control amount reaches the limit value and then becomes saturated. In this case, in such a case that the electric field strength changing width of the wireless signal entered into the antenna
501
while the automatic gain control circuit is operated is larger than, or equal to a difference (namely, sensitivity margin when AGC operation is active) between the sensitivity and the operation-starting electric field strength value of the automatic gain control (will be abbreviated as an “AGC” hereinafter) operation, and furthermore, the signal level is varied at such a pitch higher than the following speed with respect to the signal level change in the AGC operation, the electric field strength becomes lower than, or equal to the sensitivity point when the signal level is dropped. As a result, it is required to secure the sufficiently large sensitivity margin while the AGC operation is carried out.
FIG. 13
is an explanatory diagram for explaining a relationship between an operation-starting electric field strength value of an AGC operation, and both sensitivity margin when the AGC operation is performed and an IM characteristic in the continuous gain control type automatic gain control circuit.
When the operation-starting electric field strength value of the AGC operation of the automatic gain control circuit is a low level, although a calling available area (AR
3
) in the IM characteristic is increased, since the sensitivity margin is small when the AGC operation is performed, the AGC operation is weakened with respect to the field strength variation of the desirable electromagnetic wave. Also, when the operation-starting electric field strength value of the AGC operation of the automatic gain control circuit is a high level, although a calling available area (AR
2
) in the IM characteristic which can be improved by the automatic gain control circuit is decreased, since the sensitivity margin is made large when the AGC operation is performed, the AGC operation is strengthened with respect to the field strength variation of the desirable electromagnetic wave. As explained above, the operation-starting electric field value of the AGC operation must be set by considering both the IM characteristic and the sensitivity margin when the AGC operation is carried out.
Next, another conventional wireless receiver equipped with a stepped gain control type automatic gain control circuit will now be explained with reference to
FIG. 14
to FIG.
16
.
FIG. 14
is a structural diagram for showing the conventional wireless receiver equipped with the stepped gain control type automatic gain control circuit (second prior art).
In
FIG. 14
, the wireless receiver of the second prior art is arranged by employing an antenna
601
, a low noise signal amplifier (LNA)
602
, a local oscillator circuit
603
, a frequency converting circuit
604
, a Received Signal Strength Indicator (RSSI)
605
, and a gain control circuit
606
.
When a signal level of an intermediate frequency signal IF which is frequency-converted by the frequency converting circuit
604
becomes higher than, or equal to a predetermined value, the Received Signal Strength Indicator (RSSI)
605
changes a signal GC
6
to output the changed signal. The operation condition (ON-condition/OFF-condition) of the gain control circuit
606
is switched in response to the signal GC
6
derived from the Received Signal Strength Indicator
605
.
In this case, the gain control amount controlled by the gain control circuit
606
is made constant irrespective of a level of a signal entered from the antenna
601
. Also, since a large amount of gains are instantaneously controlled within one time in the stepped gain control type automatic gain control circuit, large noise may be produced when the gain is controlled (switched). As a result, normally, both the field strength
Matsushita Electric - Industrial Co., Ltd.
Pearne & Gordon LLP
Tran Congvan
Trost William
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