Detector and transmitter incorporating the detector

Details Detector and transmitter incorporating the detector Detector and transmitter incorporating the detector

2000-05-04

2001-07-24

Pascal, Robert (Department: 2817)

Amplifiers

With control of power supply or bias voltage

With control of input electrode or gain control electrode bias

C329S365000, C329S366000

Reexamination Certificate

active

06265940

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a detector for detecting the level of an output of a transmitter, such as a mobile radio transmitter, for transmitting, as its output, a high-frequency signal, and a transmitter incorporating the detector.
2. Description of the Prior Art
Referring now to
FIG. 4
, it illustrates a schematic circuit diagram showing the structure of a prior art detector used for detecting the level of an output of a transmitter for transmitting, as its output, a high-frequency signal. In the figure, reference numeral
41
denotes an input terminal to which the high-frequency signal to be detected by the detector is applied, numeral
42
denotes a capacitor having an end connected to the input terminal
41
, and numeral
43
denotes a detecting diode having an anode connected to another end of the capacitor
42
. In addition, reference numeral
44
denotes a first resistor having an end connected to a junction between the capacitor
42
and the detecting diode
43
, and another end connected to a bias supplying unit
45
for supplying a predetermined bias voltage to the detecting diode, numeral
48
denotes a capacitor having an end connected to a cathode of the detecting diode
43
and a detected voltage output terminal
46
, and another end connected to a ground, and numeral
49
denotes a second resistor having an end connected to the cathode of the detecting diode
43
and the detected voltage output terminal
46
, and another end connected to the ground. The first and second resistors
44
and
49
define a bias current flowing through the detecting diode
43
. The capacitor
48
is charged by the high-frequency signal, which has been half-wave rectified by the detecting diode
43
.
The prior art detector as shown in
FIG. 4
is so constructed as to make a bias current flow through the detecting diode
43
in order to detect a high-frequency signal at a relatively low level. The high-frequency signal to be detected is supplied from the input terminal
41
, by way of the capacitor
42
, to the anode of the detecting diode
43
. The capacitor
42
serves as a bypass capacitor to cut off the DC component of the high-frequency signal applied to the detector and to allow its high-frequency components to pass therethrough.
Unless any high-frequency signal is applied to the input terminal
41
, the bias current supplied from the bias supplying unit
45
flows through the first resistor
44
, the detecting diode
43
, and the second resistor
49
. The bias current has a value determined by the quotient of (the bias voltage from the bias supplying unit
45
− the forward voltage VF of the detecting diode
43
) by the sum of the resistances of the first and second resistors
44
and
49
.
When a high-frequency signal is applied to the input terminal
41
, the high-frequency signal passes through the bypass capacitor
42
and the sum of the voltage Vin of the high-frequency signal and the forward voltage VF is then applied to the detecting diode
43
. The waveforms of instantaneous currents flowing through the detecting diode
43
in the positive and negative halves of each cycle of the input high-frequency signal are asymmetrical to each other because the conductance of the detecting diode
43
largely varies according to the direction of the voltage across the detecting diode.
The capacitor
48
is charged by the instantaneous current flowing through the detecting diode in the positive half of each cycle. In the next negative half of each cycle, the capacitor
48
discharges and the instantaneous current therefore flows through the second resistor
49
to the ground. As a result, the total current flowing through the resistance component of the detected voltage output terminal
46
is the sum of the bias current supplied from the bias supplying unit
45
and the instantaneous current caused by the high-frequency signal. Thus the voltage signal that appears at the detected voltage output terminal
46
has a value corresponding to the level of the input high-frequency signal.
A problem with the prior art detector shown is that it has a detection characteristic showing temperature dependence, that is, the detecting diode
43
has a conductance that can vary with temperature. A change in the forward voltage VF with temperature can cause a change in the detected voltage that appears at the detected voltage output terminal
46
even though the same bias current is caused to flow through the detector.
Referring next to
FIG. 5
, it illustrates a schematic circuit diagram showing the structure of another detector as disclosed in Japanese Patent Application Publication (TOKKAIHEI) No. 8-330850, which is proposed to solve the above problem. In the figure, the same reference numerals as shown in
FIG. 4
denote the same components as of the former prior art detector, and therefore the description of these components will be omitted hereinafter. In
FIG. 5
, reference numeral
47
denotes a temperature-compensation diode having an anode connected to the cathode of a detecting diode
43
, and a cathode connected to an end of a resistor
49
, numeral
50
denotes a resistor having an end connected to a junction between the detecting diode
43
and the temperature-compensation diode
47
, and another end connected to a detected voltage output terminal
46
, numeral
51
denotes a resistor having an end connected to the cathode of the temperature-compensation diode
47
, and another end connected to the detected voltage output terminal
46
, and numeral
52
denotes a capacitor having an end connected to a junction between the detecting diode
43
and the temperature-compensation diode
47
, and another end connected to a ground. The capacitor
52
serves as a bypass capacitor for preventing a high-frequency voltage supplied to the detecting diode
43
from being supplied to the temperature-compensation diode
47
. Two diodes having the same characteristics can be used as the detecting diode
43
and the temperature-compensation diode
47
. For example, Schottky barrier diodes encapsulated in the same package are used. The first and second resistors
44
and
49
have the same resistance value.
Assuming that the sum of the resistance values of the third and fourth resistors
50
and
51
is sufficiently greater than the resistance value of the temperature-compensation diode
47
at its operating point, the bias current, which flows through the series circuit consisting of the first resistor
44
, the detecting diode
43
, the temperature-compensation diode
47
, and the second resistor
49
, has a value determined by the quotient of {the bias voltage from the bias supplying unit
45
− (the forward voltage VF of the detecting diode
43
+ the forward voltage VF of the temperature-compensation diode
47
)} by the sum of the resistance values of the first and second resistors
44
and
49
when a high-frequency signal is applied to the input terminal
41
. Since the forward voltage VF of each of the detecting and temperature-compensation diodes
43
and
47
has a negative temperature coefficient, the bias current has a positive temperature coefficient. Similarly, the voltage that appears at a junction c between the temperature-compensation diode
47
and the resistor
49
has a positive temperature coefficient. On the other hand, the voltage that appears at a junction b between the detecting diode
43
and the temperature-compensation diode
47
has a constant value equal to one-half of the bias voltage because the junction b sits right at the center of the series circuit consisting of the first and second resistors
44
and
49
, and the two diodes
43
and
47
. As a result, the DC offset voltage at the detected voltage output terminal
46
has a positive temperature coefficient because it has a value corresponding to the division of the voltage between the junctions b and c using the third and fourth resistors
50
and
51
.
When a high-frequency signal is applied to the input terminal
41
, the high-fre

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