Telecommunications – Receiver or analog modulated signal frequency converter – Measuring or testing of receiver
Reexamination Certificate
1999-11-02
2004-05-04
Tran, Pablo N. (Department: 2685)
Telecommunications
Receiver or analog modulated signal frequency converter
Measuring or testing of receiver
C327S351000, C327S352000
Reexamination Certificate
active
06731918
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a signal strength detecting device mounted on a radio communications apparatus for detecting the signal strength of a signal received by an antenna.
2. Description of Related Art
A large number of radio communications apparatuses incorporate a signal strength detecting device for detecting the signal strength of a signal received by an antenna.
In particular, in a mobile communications system employing a CDMA (Code Division Multiple Access) scheme, a base station and a mobile station each detect the signal strength of a signal transmitted from their party, so as to precisely control the strength of a signal to be transmitted to the party in accordance with the signal strength.
For example, when the base station and mobile station are far away from each other, since the signal strength of the received signal is weak, the strength of the transmitted signal is increased so that the party can receive the transmitted signal with sufficient intensity.
In contrast with this, when the base station and mobile station are close to each other, since the signal strength of the received signal is strong, the strength of the transmitted signal is reduced so that it does not interfere radio signals from other base stations or mobile stations.
FIG. 6
is a circuit diagram showing a conventional signal strength detecting device. In
FIG. 6
, the reference numeral
1
designates a logarithmic amplifier for amplifying a signal received by an antenna;
2
designates an input terminal for supplying the signal received by the antenna;
3
-
5
each designate a differential amplifier for amplifying the received signal supplied from the input terminal
2
;
6
-
8
each designate a transistor constituting the differential amplifiers
3
-
5
;
9
-
11
each designates an emitter follower for regulating the DC level of the received signal amplified by the differential amplifiers
3
-
5
; and
12
designates a current source for biasing the logarithmic amplifier
1
. The current source
12
is a constant current source whose current is proportional to the absolute temperature.
The reference numeral
21
designates an amplitude detector for detecting the signal strength of the received signal by comparing the received signal whose DC level is regulated by the emitter followers
9
-
11
of the logarithmic amplifier
1
with a reference voltage;
22
designates a reference voltage generator for generating the fixed reference voltage;
23
-
25
each designate a differential amplifier for comparing the received signal whose DC level is regulated by one of the emitter followers
9
-
11
of the logarithmic amplifier
1
with the reference voltage generated by the reference voltage generator
22
, and for producing a collector current proportional to the difference between the two;
26
-
28
each designate a transistor constituting the differential amplifiers
23
-
25
;
29
designates a capacitor for smoothing the collector current output from the differential amplifiers
23
-
25
;
30
designate a PNP current mirror circuit for inverting the polarity of the collector current smoothed by the capacitor
29
;
31
designates a resistor for converting the collector current to a voltage signal;
32
designates an output terminal for producing the voltage signal indicating the signal strength of the received signal; and
33
designates a current source for biasing the amplitude detector
21
. The current source
33
is a fixed current source whose current is proportional to the absolute temperature.
Next, the operation of the conventional signal strength detecting device will be described.
First, when the signal received by the antenna is supplied to the input terminal
2
, the differential amplifier
3
of the logarithmic amplifier
1
amplifies the received signal.
The received signal amplified by the differential amplifier
3
is output from the collectors of the transistors
6
and
7
. The received signal output from the collector of the transistor
6
is subjected to the DC component regulation by the emitter follower
9
, and then supplied to the differential amplifier
23
of the amplitude detector
21
as well as to the transistor
6
of the post-stage differential amplifier
4
. On the other hand, the received signal output from the collector of the transistor
7
is supplied to the transistor
7
of the post-stage differential amplifier
4
.
Receiving the received signal output from the differential amplifier
3
, the differential amplifier
4
of the logarithmic amplifier
1
further amplifies the received signal.
The received signal amplified by the differential amplifier
4
is output from the collectors of the transistors
6
and
7
. The received signal output from the collector of the transistor
6
is subjected to the DC component regulation by the emitter follower
10
, and then supplied to the differential amplifier
24
in the amplitude detector
21
as well as to the transistor
6
in the post-stage differential amplifier
5
. On the other hand, the received signal output from the collector of the transistor
7
is supplied to the transistor
7
in the post-stage differential amplifier
5
.
Receiving the received signal output from the differential amplifier
4
, the differential amplifier
5
in the logarithmic amplifier
1
further amplifies the received signal.
The received signal amplified by the differential amplifier
5
is output from the collector of the transistor
6
. The received signal output from the collector of the transistor
6
is subjected to the DC current regulation by the emitter follower
11
, and then supplied to the differential amplifier
25
in the amplitude detector
21
.
Receiving the received signal amplified by the differential amplifiers
3
-
5
in the logarithmic amplifier
1
, the differential amplifiers
23
-
25
in the amplitude detector
21
compare the received signal with the reference voltage generated by the reference voltage generator
22
, and output the collector currents I
c
proportional to the difference between the two.
The collector currents I
c
output from the differential amplifiers
23
-
25
are smoothed by the capacitor
29
, undergo the polarity inversion by the PNP current mirror circuit
30
, and are converted by the resistor
31
to a voltage signal (that indicates the signal strength of the received signal) to be output from the output terminal
32
.
Here, the reason will be described for using the fixed current source proportional to the absolute temperature as the current source
12
for biasing the logarithmic amplifier
1
.
First, the gain characteristic of the differential amplifiers
3
-
5
in the logarithmic amplifier
1
is given by the following expression.
G=(q
I/k
T)
R
L
where G is the gain, q is the elementary charge, I is the magnitude of the collector current, k is the Boltzmann constant, T is the absolute temperature, and R
L
is a load resistance.
If the logarithmic amplifier
1
is biased by a current source without temperature dependence, the collector current I will be fixed, and the gain G of the differential amplifiers
3
-
5
will be reduced in inverse proportion to the absolute temperature T.
However, this will reduce the gain G of the differential amplifiers
3
-
5
, making it impossible to amplify the received signal to a desired level. Accordingly, the collector current I must be made proportional to the absolute temperature T.
In view of this, the fixed current source with temperature dependence is used to provide the logarithmic amplifier
1
with the bias current proportional to the absolute temperature T.
Thus, the conventional signal strength detecting device with the foregoing configuration can amplify the received signal by means of the logarithmic amplifier
1
without being affected by temperature change. However, since the current source
33
for biasing the amplitude detector
21
also consists of the constant current source whose current is proportional to the absolute temperature T, even if the signal streng
Burns Doane Swecker & Mathis L.L.P.
Renesas Technology Corp.
Tran Pablo N.
LandOfFree
Signal strength detecting device with little temperature... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Signal strength detecting device with little temperature..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Signal strength detecting device with little temperature... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3199086