JP2906708B2 - Automatic level control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an automatic level control (AL)
C) The present invention relates to a circuit, and more particularly to an ALC circuit for controlling a transmission power level by a transmission level control signal in a transmission power amplifier for mobile communication.

[0002]

2. Description of the Related Art In a mobile communication system using a cellular system, transmission power varies depending on the distance between a base station and a mobile station in the same cell. In order to adjust this imbalance, each mobile station needs a transmission power control function. In addition, the time from the reception of the incoming call signal to the rise of the transmission power is strictly determined for airline control (for example, for such a method, refer to “NMT DOC900-3janua”.
ry1985]. A) An ALC circuit meeting these two conditions must be realized.

Conventionally, this type of ALC circuit has a directional coupler 2 connected to the output of a transmission power amplifier 1 as shown in FIG.
, And the difference between the result and the transmission level control signal is detected by the operational amplifier 3.
This has been realized by forming a feedback loop for controlling the gain of the transmission power amplifier 1 via the converter 101 and the transistor 10.

The rise time for airline control is determined by the loop gain of the feedback loop and the frequency characteristics of the operational amplifier 3. This frequency characteristic is stable because it is determined by the resistance and the capacitor in the operational amplifier 3. On the other hand, the loop gain is affected by the characteristics of the base voltage and the collector current of the transistor 10, and therefore, is very unstable without the VI conversion circuit 101. Therefore, the VI conversion circuit 101 is inserted, and the base current-collector current characteristic (h _fe ) of the transistor 10 is used, so that the transistor 10 becomes stable. However, the transistor h _fe is not suitable for mass production as it is because it is about 50 to 200 due to manufacturing variations. Therefore, a double loop system including a minor loop inside as shown in FIG. 3 which is usually performed by automatic control is adopted for the feedback loop, and the VI conversion circuit 101 is also used as shown in FIG. A circuit in which a constant current circuit and a current mirror are combined may be employed. The circuit improved in this way is the circuit diagram of FIG.

[0005] In the circuit of FIG.
The I-converter 101 and the transistor 10 form a minor loop, and the feedback loop compensates for variations in h _fe of the transistor 10. Therefore, the loop gain constituted by the operational amplifier 103, the minor loop system, the transmission power amplifier 1 and the directional coupler 2 is not affected by manufacturing variations, and a stable transmission power rising characteristic can be obtained.

[0006]

Generally, a mobile station such as a portable telephone uses a battery as a power source, so that the operational amplifiers 103 and 104 shown in FIG. 5 operate with a single power source. On the other hand, the in-phase input range of the operational amplifier is generally limited to a certain range centered on the center of the power supply voltage. Normal operation cannot be expected with an input voltage exceeding this range, and in the worst case, a malfunction occurs. Similarly, the output voltage range of the operational amplifier becomes about 0.5 V to 1 V lower than the power supply voltage and the ground level.

Therefore, when the circuit shown in FIG. 5 is used with a single power supply, the operating point is at the ground level, and the rise time of the transmission power amplifier varies and becomes unstable.

[0008] Mobile communication uses radio waves as a communication medium, and its frequency resources are limited. It must be absolutely avoided to consume it with radiation from an unnecessary transmission power amplifier.

[0009]

According to the present invention, there is provided a first operational amplifier which receives an output of a directional coupler connected to an output of a transmission power amplifier and a transmission level control signal, and the first operational amplifier. A second operational amplifier receiving the output of the operational amplifier, a third operational amplifier receiving the output of the second operational amplifier, and a first transistor connected between the input and output of the third operational amplifier And the third operational amplifier input and the third
, A fourth transistor connected to the third transistor by a current mirror connection, and a transmission power level of the transmission power amplifier is controlled by a current flowing through the fourth transistor. And an automatic level control circuit for adding a voltage generated by a current flowing through the fifth transistor to an input of the second operational amplifier.

[0010]

Next, the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of an ALC circuit used in a portable telephone according to an embodiment of the present invention. In FIG. 1, the transmission power amplifier 1 includes a drive unit 50 and an output unit 60, and is supplied to the drive unit 50 because it does not need to be a linear power amplifier because it uses an FM signal that is constant amplitude modulation. The transmission power gain can be varied by controlling the power supply voltage. The directional coupler 2 is coupled by a strip line, rectified by a pin diode, and inputs a DC level proportional to the transmission power to the operational amplifier 3. The operational amplifier 3 amplifies the difference between the input level and the transmission level control signal, and inputs its output to the operational amplifier 4 with a frequency characteristic determined by CR. The DC level output from the directional coupler 2 always has an offset of about 1 to 1.5 V due to a pin diode or the like. Therefore, the operational amplifier 3 does not malfunction due to the limitation of the common mode input range. The operational amplifier 4 sets its operating point at 1 /
Since it is 2V _DD , it operates in the common mode input range. The operational amplifier 5 to which the output of the operational amplifier 4 is input also has an operating point at Ｖ _VDD , and a current determined by the input resistance flows through the transistors 7 and 6. The transistors 7 and 6 are P-channel MOSFETs, and their gates are commonly connected, so that the same current flows. Therefore N
The current also flows through the channel type MOS transistor 8. Since the transistors 8 and 9 have a channel width ratio of 1: n, the current of the transistor 9 flows n times as large. The base current of the transistor 10 is controlled by the current, and the voltage applied to the driving unit 50 of the transmission power amplifier 1 is controlled. Since this voltage is also applied to the operational amplifier 4 at the same time, a minor loop is formed, and the variation due to h _fe of the transistor 10 is compensated.

[0012] In a portable telephone, miniaturization and low power consumption are required. Therefore, it is desirable to constitute the IC with one chip as much as possible. However, since a power supply current of about 200 mA generally flows through the drive unit 50 of the transmission power amplifier 1, it is more efficient to use the transistor 10 as an individual component. Therefore, in this embodiment, the operational amplifiers 3 to 5 and the transistors 6 to 9 are configured as one chip of a CMOS process and
An LC circuit is realized.

[0013]

As described above, according to the present invention, since all the operational amplifiers operate within the common-mode input range, the rise time of the transmission power amplifier varies or becomes unstable even with a single power supply operation of a portable telephone or the like. It is possible to realize the transmission power control function and the transmission power start-up operation for the air line control without becoming a problem. In general, a 90% rise time needs to be performed within 1 msec in a car phone, but in this embodiment, even if h _fe varies between 50 and 200, it is 0.4 to 0.6.
In msec, the transmission power amplifier can be stably started without oscillation. Therefore, there is an effect that it is possible to provide a mobile terminal that does not emit unnecessary radio waves in mobile communication using radio waves as a communication medium and using limited frequency resources.

Further, there is an effect that an ALC circuit can be realized in a one-chip IC as a part of a circuit requiring small size and low power consumption such as a portable telephone.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of an ALC circuit used in a mobile phone according to one embodiment of the present invention.

FIG. 2 is a circuit block diagram of a conventional ALC circuit.

FIG. 3 is a block diagram showing a double loop type feedback loop for automatic control.

FIG. 4 is a circuit diagram of a commonly used VI conversion circuit.

FIG. 5 is a circuit diagram of an ALC circuit obtained by combining FIGS. 3 and 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transmission power amplifier 2 Directional coupler 3-5 Operational amplifier 6-10 Transistor 50 Drive part 60 Output part 101 VI conversion circuit 103-104 Operational amplifier

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-57-113634 (JP, A) JP-A-63-136703 (JP, A) JP-A 2-21830 (JP, U) JP-A 58-113 30342 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) H04B 1/04

Claims (2)

(57) [Claims] 1. A first signal receiving an output of a directional coupler connected to an output of a transmission power amplifier and a transmission level control signal.
An operational amplifier, a second operational amplifier having the input of the first operational amplifier as an input, a third operational amplifier having the input of the second operational amplifier as an input, and an input / output of the third operational amplifier. A third transistor connected between the first transistor and the third transistor
A second transistor connected between the operational amplifier input of the third transistor and the third transistor, a fourth transistor connected to the third transistor by a current mirror connection, and a current flowing through the fourth transistor. A fifth transistor for controlling a transmission power level of the amplifier, wherein a voltage generated by a current flowing through the fifth transistor is added to an input of the second operational amplifier. . 2. The first to third operational amplifiers and a first operational amplifier
2. The automatic level control circuit according to claim 1, wherein the first to fourth transistors are formed by one-chip integrated circuits.