JP3351067B2 - Detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to temperature compensation of a detection circuit composed of diodes, and is used, for example, for a high-frequency power detector such as a radio transmitter.

[0002]

2. Description of the Related Art For example, in a transmitter of a mobile telephone radio, the power level of an output signal is strictly specified. Therefore, the power level is detected and feedback control is performed so that the power level falls within the specification. It is carried out. And
As a detection circuit for detecting the power level of this output signal,
An envelope detector as shown in FIG. 4A is generally used. Further, a detection circuit which has a wide dynamic range of an output signal to detect and detects a power level of a small output signal uses a diode biased as shown in FIG. 4B.

[0003]

However, in the conventional circuit described above, for example, in the detection circuit of FIG. 4A, when the ambient temperature rises, the output voltage changes due to the temperature characteristics of the diode and the like. There is a problem that accurate detection cannot be performed. Also in the detection circuit of FIG. 4B, the bias voltage changes due to the temperature characteristics of the diode in addition to the problem of FIG. 4A, and as a result, the error of the detection output increases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a detection circuit in which a detection error due to a temperature characteristic of a diode is improved and temperature compensation is performed.

[0005]

Therefore, the present invention provides a detection circuit using a diode, comprising: a detection diode provided on a line from a detection input terminal to a detection output terminal; and a detection output terminal side of the detection diode. And a power supply connected to the detection input terminal side of the detection diode, and a power supply connected to the detection diode. A first resistor provided between the power supply and the power supply, and the same as the first resistor
A resistance value, and an impedance from the detection output terminal to the ground through the temperature compensation diode is equal to the impedance from the detection output terminal to the power supply through the detection diode. 2, a first capacitor provided between the detection diode and the detection input terminal, and an impedance from the detection output terminal to the ground via the temperature compensation diode and the first resistor. And a second capacitor provided to be equal to the impedance from the detection output terminal to the detection input terminal via a first resistor.

[0006]

With the above arrangement, the first and second resistances are equal.
The impedance from the power supply to the detection output terminal via the detection diode is equal to the impedance from the ground to the detection output terminal via the temperature compensation diode because of the resistance value , and the detection diode and the temperature compensation diode Means that the electrical characteristics with respect to the temperature change are equal. Therefore, the change in impedance due to the temperature change similarly changes, and even when the ambient temperature changes, the voltage of the detection output terminal based on the power supply voltage is always constant.

Further, when a signal is input to the detection input terminal, the impedance from the power supply to the detection output terminal via the detection diode and the first resistor and the ground to the temperature in the equivalent circuit accompanying the signal input. The impedance to the detection output terminal via the compensation diode and the second resistor is equalized by the first and second capacitors, and the detection diode and the temperature compensation diode have electrical characteristics with respect to temperature change. Both are equal. Therefore, the detection circuit of the present invention can extract an accurate output voltage based on the input signal without being affected by a change in the ambient temperature.

[0008]

As described above, the present invention has an excellent effect that the detection error due to the temperature characteristic of the diode can be improved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to an embodiment shown in the drawings. First, the detection circuit of the present invention is configured inside a transmitter of a mobile telephone radio shown in FIG. 5 as a specific application. In FIG. 5, a high-frequency amplifier 21 receives a high-frequency signal from a modulation unit (not shown), amplifies the input high-frequency signal, and outputs the high-frequency signal. A detection circuit 1 for detecting the signal level of the high-frequency signal output from the ASIC and outputting a voltage value corresponding to the detected signal level;
The control unit 22 controls the amplification factor of the high-frequency amplifier 21 based on the voltage value output from the detection circuit 1. That is, in the transmitter of the mobile telephone radio, the signal level detected by the detection circuit 1 is detected by the detection circuit 1 in order to strictly define the signal level output from the antenna 23, and the control is performed based on the detected signal level. The configuration is such that feedback control for controlling the high-frequency amplifier 21 is performed so that the unit 22 falls within the regulation. The present invention relates to a circuit configuration of the detection circuit 1 provided inside the transmitter.

FIG. 1 is a configuration diagram of a detection circuit showing a first embodiment of the present invention. In FIG. 1, an Rf input terminal 2 is an input terminal for receiving a high-frequency signal, and an anode 4 of a detection diode 4 via a DC cut capacitor 3.
a. There is a branch point between the capacitor 3 and the detection diode 4, and this branch point is connected to the resistor 5
, And a branch point between the resistor 5 and the power supply 6 is grounded via a capacitor 11. On the other hand, the cathode 4b of the detection diode 4 is
The detection output terminal 7 is connected to the detection output terminal 7 and is connected between the detection diode 4 and the detection output terminal 7 as shown in FIG.
There are two branches, one for the load diode 8 and one for the resistor 1
The other is grounded via a load capacitor 9 to the ground. The detection diode 4 is DC-biased via a resistor 5, a load diode 8, and a load resistor 10.

If the resistance 5 and the resistance 10 have the same resistance value, and the detection diode 4 and the load diode 8 have the same electrical and temperature characteristics, the direct current can be reduced.
The impedance from the detection output terminal 7 to the power supply 6 is equal to the impedance from the detection output terminal 7 to the ground. Therefore, even if the forward voltage drops V _F4 and V _{F8 of} the detection diode 4 and the load diode 8 change with temperature, if they are arranged so as to be equal in temperature, V _F4 = V _F8 . Since the output terminal 7 always shows a potential of 1/2 of the power supply voltage 6 in a DC manner, a change in the output voltage due to a DC temperature characteristic of the detection output can be eliminated. That is, since the change in the output voltage due to the DC temperature characteristic can be eliminated, the offset voltage (bias voltage) of the detection output when the bias is applied hardly changes. As described above, since the detection diode 4 is biased, it is possible to detect a small signal, and it is possible to eliminate the influence on the detection output due to the fluctuation of the offset voltage of the detection output.

Next, a case where a high-frequency signal is input to the detection circuit having the above configuration will be described. First, Rf
When a negative half-wave of a high-frequency signal is applied to the input terminal 1, the capacitor 3 is charged via the resistor 5. Next, when a positive half-wave is applied, the charged capacitor 3
Is charged in the capacitor 9 via the detection diode 4. Then, discharge is performed through the load diode 8 and the resistor 10 in the next negative half cycle. FIG. 2 shows an equivalent circuit for one cycle when the high-frequency signal is input. Here, if the capacitors 3 and 9 have the same capacitance, the impedance from the detection output terminal 7 to the Rf input terminal 2 is equal to the impedance from the detection output terminal 7 to the ground when a high-frequency signal is input. Become.

That is, even if the characteristics of the detection diode 4 and the load diode 8 change with temperature, if they are arranged so as to be equal in temperature, the same effect as that of the above-described direct current can be expected. The output voltage based on the generated high-frequency signal does not change with temperature. As described above, the detection circuit of the present invention is a circuit that can output a voltage that is very stable against a change in temperature.

Next, a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, as shown in FIG. 3, the resistor 5 connected to the branch point between the capacitor 3 and the detection diode 4 is different from the first embodiment in that the resistor 12 and the resistor 13 are connected. It is different in that it is connected to the point where the voltage is divided. Therefore, by arbitrarily changing the resistance 12 and the resistance 13, the offset voltage input to the detection diode 4 can be set to a desired value. As a result, the offset voltage of the detection output can be set to a desired value. it can.

In the second embodiment, as in the first embodiment, there is an excellent effect that a very stable voltage can be output with respect to a temperature change. Therefore, from the above, the resistances 5 and 10 that make the impedance from the detection output terminal 7 to the power supply 6 equal to the impedance from the detection output terminal 7 to the ground in a DC manner are formed. By configuring the capacitors 3 and 9 to make the impedance from the detection output terminal 7 to the signal source (Rf input terminal 2) equal to the impedance from the detection output terminal 7 to the ground,
Even if the ambient temperature changes, the output voltage does not change due to the temperature characteristics of the diode, and an accurate output voltage can be detected.

In the embodiment described above, the resistance 5
Resistance of the capacitor 3 and the capacitor 10, and the capacitor 3 and the capacitor 9
Are the same, but are not necessarily limited to the same value in consideration of the power supply 6 and the signal source impedance. The impedance up to the ground may be made substantially equal.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram when a high-frequency signal is input in the first embodiment.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing a conventional detection circuit.

FIG. 5 is a configuration diagram showing the inside of a transmitter provided with a detection circuit.

[Explanation of symbols]

 3 Capacitor 4 Detection diode 5 Resistance 6 Power supply 8 Load diode 9 Capacitor

Claims (1)

(57) [Claims] 1. A detection circuit using a diode, comprising: a detection diode provided on a line from a detection input terminal to a detection output terminal; and a detection diode connected to the detection output terminal side of the detection diode.
And a temperature compensation diode provided so that electrical characteristics with respect to a temperature change are equal to those of the detection diode, a power supply connected to the detection input terminal side of the detection diode, and the detection diode and the power supply. The first provided between
And the same resistance as the first resistor, the impedance from the detection output terminal to the ground via the temperature compensation diode, and the impedance from the detection output terminal to the power supply via the detection diode A second resistor provided so as to be equal in comparison; a first capacitor provided between the detection diode and the detection input terminal; a temperature compensation diode from the detection output terminal; A second impedance provided from the detection output terminal to the detection diode via the first resistor and the impedance from the detection output terminal to the detection input terminal via the first resistor. A detection circuit, comprising: a capacitor;