JPH04358409A - Transmission power control circuit for radio communication equipment - Google Patents

Abstract

PURPOSE:To always secure the transmission power by keeping the loop gain of a feedback loop at a constant level despite a two-stage constitution of a variable gain circuit. CONSTITUTION:A 1st variable attenuator 11 is provided in series to a 2nd variable attenuator 1 followed by a gain control-circuit 3. These attenuators 11 and 1 form a transmission power control circuit which transmits a transmission signal after control of the level of the signal and the amplification of power. A variable gain amplifier 12 is provided in a feedback loop of the circuit 3, and the gain of the amplifier 12 is varied in accordance with the gain varying operation of the attenuator 11.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to a transmission power control provided to vary transmission power in a radio communication device used in a mobile radio communication system such as a mobile/automobile radio telephone system or a cordless radio telephone device. Related to circuits.

0002

2. Description of the Related Art Conventionally, as one type of mobile radio communication system, for example, a cellular type portable radio communication system has been operated. For example, as shown in FIG. 5, this type of system includes a control station CS connected to a wired telephone network NW, and a plurality of base stations BS1 to BS1 connected to the control station CS via wired lines CL1 to CLn, respectively. BSn and a plurality of mobile stations PS1 to PSm. Each of the base stations BS1 to BSn forms wireless zones E1 to En, generally called cells, in different areas. Mobile station P
S1 to PSm are connected to the base station of the cell in which they are located via an empty wireless communication channel, and further connected from this base station to the wired telephone network NW via the control station CS. Further, when the mobile stations PS1 to PSm move to another cell during communication, the base station to which they are connected is switched to the base station of the cell to which they are moving while continuing communication.

[0003] By the way, the wireless communication device for a mobile station used in such a system has a method for controlling the transmission power of its own station based on transmission power designation information transmitted from the base station BS when setting up a wireless line, for example. There are some that are equipped with a circuit to do this. FIG. 4 is a circuit block diagram showing an example of the configuration. In the figure, this circuit includes a variable attenuator 1, a power amplifier 2, and a gain control circuit section 3. First of all, the variable attenuator 1 provides an attenuation amount based on an attenuation control signal supplied from the gain control circuit section 3 to the input transmission signal and outputs the signal. The power amplifier 2 amplifies the power of the transmission signal output from the variable attenuator 1, and this amplified transmission signal is transmitted from an antenna (not shown).

On the other hand, a part of the transmission signal output from the power amplifier 2 is guided to the gain control circuit section 3 via the directional coupler 4. The gain control circuit section 3 includes a detector 6, a smoothing circuit 7, a comparison amplifier 8, a reference voltage generator 9, and a low-pass filter 10. The transmit signal outputted from the power amplifier 2 is detected by the wave detector 6 and smoothed by the smoothing circuit 7 to detect the transmit signal level. A comparator amplifier 8 compares the difference between the two and detects the difference. Then, by negatively feeding back a signal corresponding to this difference to the variable attenuator 1 via the low-pass filter 10,
The amount of attenuation of the variable attenuator 1 is varied.

With such a configuration, if the reference voltage value of the reference voltage generator 9 is variably set to a predetermined value in accordance with the transmission power designation information transmitted from the base station, the gain control circuit section 3 can variably set the reference voltage value to a predetermined value. The amount of attenuation of the attenuator 1 is variably controlled, so that the power of the transmitted signal is set to a value specified by the base station.

[0006] Generally speaking, in order to variably control the transmission power of a transmission signal to a required level in this type of transmission power control circuit, it is practically necessary to provide the level control stage with a fairly wide level control range. However, in a transmission power control circuit having only one stage of variable attenuator, as in the circuit described above, there is a limit to the range of level adjustment, and for this reason, it is difficult to variably control the signal level of the transmission signal to a desired level. There was a case.

[0007] Considering the above circumstances, for example, FIG.
As shown in the figure, a variable attenuator 11 is provided before the variable attenuator 1, and after the first stage variable attenuator 11 gives a certain amount of attenuation to the transmitted signal, the second stage variable attenuator 1 attenuates the transmitted signal. Furthermore, a transmission power control circuit has been proposed in which a sufficient level control width of the transmission signal is ensured by providing an amount of attenuation. In this transmission power control circuit, a control circuit (not shown) supplies a control signal to the reference voltage generator 9 to variably control the reference voltage value in accordance with transmission power designation information from the base station, and also controls the reference voltage value by variable attenuator 9. By supplying different control signals to 11 and variably controlling the amount of attenuation, the total amount of attenuation for the transmission signal is set.

[0008] Regarding the allocation of attenuation to each variable attenuator 1, 11, for example, if the amount of attenuation is increased to variable attenuator 11 and less to variable attenuator 1, it becomes possible to control the transmission power more accurately. .

[0009]

However, when attempting to control the level of transmission power in a circuit in which variable attenuators are provided in two stages, the following problem occurs. That is, the loop gain of the feedback loop including the second variable attenuator 1 changes depending on the transmission power of the transmission signal output from the first attenuator 11. Therefore, during communication, the setting of the first variable attenuator 11 changes based on a transmission power change instruction from the base station BS, and as a result, the transmission power of the transmission signal output from the first variable attenuator 11 changes. If it changes, problems with the control system will occur, such as slowing down the response speed of the feedback loop and increasing the error with respect to the set value of the transmission output. In other words, changes in the loop response characteristics and steady-state error of the feedback loop occur. Also,
In some cases, the feedback loop may oscillate and radiate unnecessary waves during transmission, which may cause problems such as interference with other wireless devices, which is extremely undesirable.

Therefore, an object of the present invention is to provide a variable gain circuit with two
It is an object of the present invention to provide a transmission power control circuit for a wireless communication device, which can maintain a constant loop gain of a feedback loop even in a stage configuration, and thereby can always generate stable transmission power.

[0011]

[Means for Solving the Problems] In order to achieve the above object, the present invention includes at least one stage of first variable gain circuit that varies and outputs the power of a transmission signal according to a first control signal; a second variable gain circuit that varies and outputs the power of the transmission signal output from the first variable gain circuit; and a signal level that corresponds to the power of the transmission signal output from the second variable gain circuit. a gain control circuit that generates a second control signal for detecting the signal level, compares the signal level with a reference signal level, and brings the difference close to zero, and supplies the second control signal as feedback to the second variable gain circuit; Equipped with variable loop gain circuit. The variable loop gain circuit is configured to vary the loop gain of the gain control circuit in response to the variable gain operation of the first variable gain circuit caused by the first control signal.

0012

[Action] As a result of taking the above measures, the following effects occur. That is, in response to the gain variable operation of the first variable gain circuit by the first control signal, the loop gain of the gain control circuit is varied to compensate for the change in the loop gain due to the change in the gain of the first variable gain circuit. Since the loop gain is controlled, the loop gain is always kept constant regardless of the change in the gain of the first variable gain circuit. Therefore, it is possible to prevent a decrease in the response speed of the feedback loop of the gain control circuit and an increase in error with respect to the set value of the transmission power, and as a result, it is possible to perform transmission power control with excellent responsiveness and high precision. At the same time, the problem of radiating unnecessary waves and causing trouble to other wireless devices is also eliminated. Thereby, it is possible to realize a transmission power control circuit for a wireless communication device in which the transmission power is always stable.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit block diagram showing the configuration of a wireless communication device equipped with a transmission power control circuit according to an embodiment of the present invention. This device is roughly divided into a transmission system, a reception system, and a control system. Note that 30 is a battery as a power source.

The transmission system includes a transmitter 13 and a speech encoder (S
PCOD) 14 and error correction coder (CHCOD) 15
, a digital modulator (MOD) 16 , a mixer 17 , a transmission power control circuit (PA) 18 , a high frequency switch circuit (SW) 19 , and an antenna 20 . The speech encoder 14 encodes the transmission signal output from the transmitter 13. The error correction encoder 15 performs error correction encoding on the digitized transmission signal outputted from the audio encoder 14 and the digitized control signal outputted from a control circuit 26, which will be described later. In the digital modulator 16, the intermediate frequency signal is subjected to QPSK modulation, for example, using the digitized transmission signal output from the error correction encoder 15. In the mixer 17, this modulated intermediate frequency signal is mixed with the local oscillation signal output from the frequency synthesizer 27, and the frequency is converted into a high frequency signal. In the transmission power control circuit 18, the high frequency transmission signal output from the mixer 17 is amplified to a predetermined transmission power. The high frequency switch 19 is connected to the control circuit 2
6, it becomes conductive only for the period of the designated transmission time slot, and during this period, the transmission high frequency signal output from the transmission power control circuit 18 is supplied to the antenna 20, and is transmitted from this antenna 20 toward the base station BS. do.

On the other hand, the receiving system includes a receiver (RX) 21
, a digital demodulator (DEM) 22, an error correction decoder (CHDEC) 23, and a speech decoder (SPDEC) 2
4 and a receiver 25. In the receiver 21,
Radio reception waves received by antenna 20 and high frequency switch 19 in a predetermined reception time slot are frequency-converted into intermediate frequency signals. The digital demodulator 22 performs bit synchronization and frame synchronization with respect to the received intermediate frequency signal output from the receiver 21, and then
Digital demodulation of this received intermediate frequency signal is performed. In the error correction decoder 23, the digital demodulated signal output from the digital demodulator 22 is subjected to error correction decoding. The digitized reception signal obtained by this error correction decoding is output to the audio decoder 24, and the digitized control signal is supplied to the control circuit 26. The audio decoder 24 decodes the digitized received signal. Then, the analog reception signal restored by this decoding process is amplified and outputted from the receiver 25.

The control system also includes a control circuit (CONT) 26
, a frequency synthesizer (SYN) 27, a received field strength detection circuit (RSSI) 28, and a transmission request switch 29
It is equipped with Frequency synthesizer 27 generates a local oscillation frequency corresponding to the wireless channel designated by control circuit 26. The received field strength detection circuit 28 detects the received field strength of the radio wave transmitted from the base station BS, and supplies the detection signal to the control circuit 26.

The control circuit 26 is equipped with, for example, a microcomputer as a main control section, and has transmission power control means in addition to normal control functions such as wireless line connection control and call control. This transmission power control means includes first and second controls for variably controlling the transmission power according to the transmission power designation information transmitted from the base station when a wireless line is connected or during a call. It generates signals and supplies these control signals to a transmission power control circuit 18, which will be described later. Note that each of the above control signals is converted into an analog signal by a D/A converter (not shown) and then supplied to the transmission power control circuit 18.

By the way, the transmission power control circuit 18 is configured as follows. FIG. 2 is a circuit block diagram showing its configuration. In this figure, the same parts as those in FIG. 3 are given the same reference numerals and detailed explanations will be omitted.

In the figure, a variable gain amplifier 12 is interposed between a comparator amplifier 8 and a low-pass filter 10. A first control signal output from the control circuit 26 is supplied to the variable gain amplifier 12 together with the first variable attenuator 1. That is, the attenuation variable operation of the first variable attenuator 11 and the gain variable operation of the variable gain amplifier 12 are performed in a relationship with each other.

With such a configuration, let us now assume that transmission power instruction information arrives from the base station BS and that the control circuit 26 generates first and second control signals in response to this information. Then, in the transmission power control circuit 18,
The reference voltage value of the reference voltage generator 9 is set to a predetermined value by the second control signal, and thereafter the feedback loop adjusts the attenuation amount of the second variable attenuator 1 so that the transmission detection level becomes equal to this reference value. control the feedback.

On the other hand, the attenuation amount of the first variable attenuator 11 is set by the first control signal to a value specified by the first control signal. Therefore, from now on, the transmitted signal is attenuated by the amount of attenuation set in the first variable attenuator 11 and then supplied to the second variable attenuator 1. That is, the transmission signal whose signal level has been changed by the first variable attenuator 11 is input to the second variable attenuator 1. For the feedback loop including the second variable attenuator 1, this change in the input level of the transmission signal causes a change in the loop transfer function.

That is, for example, the output high frequency power of the power amplifier 2 is vout, the input high frequency voltage of the power amplifier 2 is vin, and the DC detection voltage output from the smoothing circuit 7 is VD.
ET, the reference voltage is VREF, the DC control voltage of the second variable attenuator 1 is VCONT, and the input high frequency voltage of the second variable attenuator 1 is v', then vout, V
DET, VCONT, and vin are each vout = K0 ・vin

...(1) VDET = K1 ・
vout
...(2) V
CONT=K2 ・(VREF -VDET)+VR
EF...(3)
vin =K3 v'・VCONT
…
(4)

It is expressed as follows. Note that K0 to K3 are the power amplifier 2, the detector 6, the comparison amplifier 8, and the second
represents the control gain of the variable attenuator 1. In the above equation, each control system is assumed to be linear. Furthermore, it is assumed that the frequency characteristics of the feedback loop are determined by the frequency characteristics F(S) of the low-pass filter 10, and the frequency characteristics of each control system described above are omitted as they do not affect the inside of the loop.

Therefore, from the above equations (1) to (4), the feedback loop transfer function (closed loop transfer function) H(S) and the open loop transfer function (open loop transfer function) G(S) are as follows.
It is expressed as follows. H(S)=VDET/VREF Almost equal G(S)/(1+G(S))


...(5) G(S)=K0 K1 K2
K3 v'F(S)
...(6)

As can be seen from equation (5), G(S) is the input high frequency voltage v of the second variable attenuator 1.
Since there is a term ', G(S) changes due to this v'. This v' is the input high frequency voltage v of the first variable attenuator 11
Expressed using the attenuation amount K4, which is the control gain,
v'=K4 ・v・VCONT

…(7)

[0026] In other words, when the attenuation amount K4 of the first variable attenuator 11 is changed, the input high frequency voltage v' of the second variable attenuator 1 changes by the amount of change, and as a result, the closed loop transfer function H(S), and the open-loop transfer function G(S) will change. These changes in transfer characteristics are undesirable because they cause problems such as a decrease in loop response speed and an increase in errors.

However, in the transmission power control circuit 18 of this embodiment, the gain of the variable gain amplifier 12 in the feedback loop is changed depending on the first control signal by the change in the attenuation amount of the first variable attenuator 11. Variable control is performed to compensate for changes in gain. That is, the relationship between the attenuation amount K4 of the first variable attenuator 11 and the gain K2 of the feedback loop is as follows.
K4 /K2 = α (α is a constant)
…(
8).The gain is controlled so that Therefore, the feedback loop gain is always kept constant regardless of the setting change of the attenuation amount K4 of the first variable attenuator 11.

In this way, in this embodiment, the variable gain amplifier 12 is provided in the feedback loop that controls the second variable attenuator 1, and at the same time the attenuation amount of the first variable attenuator 11 is variably controlled. Since the gain of the variable gain amplifier 12 is variably controlled, the problem that the loop gain of the feedback loop changes depending on the amount of attenuation of the first variable attenuator 11 is eliminated. For this reason, the response speed of the feedback loop decreases,
It is possible to prevent an increase in error with respect to the set value of transmission power, and thereby it is possible to perform transmission power control with excellent responsiveness and high accuracy. Furthermore, the problem of radiating unnecessary waves and causing trouble to other wireless devices is also eliminated.

Note that the present invention is not limited to the above embodiments. For example, in the above embodiment, variable attenuators 1 and 11
Although the explanation has been given by taking a circuit using a variable gain amplifier as an example, it is also applicable to a circuit using a variable gain amplifier, for example. Furthermore, in the embodiment described above, the variable gain amplifier 12 was provided between the comparison amplifier 8 and the low-pass filter 10, but the comparison amplifier may be of a variable gain type and configured to vary its gain. In addition, it goes without saying that various modifications can be made to the circuit configuration of the gain control circuit that controls the transmission power, the configuration of the circuit that varies the loop gain, etc. without departing from the gist of the present invention.

[0030]

Effects of the Invention When the gain of the first variable gain circuit is varied, the loop gain of the feedback loop including the second variable gain circuit is equal to or smaller than the loop gain caused by the change in the gain of the first variable gain circuit. Since it is variably controlled to compensate for the change in
It is possible to provide a transmission power control circuit for a wireless communication device that can maintain the loop gain of the feedback loop constant and thereby always generate stable transmission power.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram showing the configuration of a wireless communication device having a transmission power control circuit according to an embodiment of the present invention.

FIG. 2 is a circuit block diagram showing the configuration of a transmission power control circuit in the apparatus shown in FIG. 1.

FIG. 3 is a circuit block diagram showing an example of a conventional transmission power control circuit.

FIG. 4 is a circuit block diagram showing another example of a conventional transmission power control circuit.

FIG. 5 is a schematic configuration diagram showing an example of a mobile radio communication system.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1, 11... Variable attenuator, 2... Power amplifier, 3... Gain control circuit part, 4... Directional coupler, 5... Terminator, 6... Detector,
7... Smoothing circuit, 8... Comparison amplifier, 9... Reference voltage generator,
10...Low pass filter, 12...Variable gain amplifier, 13
...Telephone, 14...Speech encoder (SPCOD), 15...Error correction coder (CHCOD), 16...Digital modulator (MOD), 17...Mixer, 18...Transmission power control circuit (
PA), 19...High frequency switch circuit (SW), 20...Antenna, 21...Receiver (RX), 22...Digital demodulator (DEM), 23...Error correction decoder (CHDEC),
24...Speech decoder (SPDEC), 25...Handset, 26
...Control circuit, 27...Frequency synthesizer (SYN), 2
8... Received field strength detection circuit (RSSI), 29... Transmission request switch, 30... Battery.

Claims (1)

[Claims] Claims: 1. At least one stage of first variable gain circuit that varies and outputs the level of a transmission signal according to a first control signal, and the level of the transmission signal output from the first variable gain circuit. A second variable gain circuit outputs a variable gain circuit, and a signal level corresponding to the power of the transmission signal outputted from the second variable gain circuit is detected, and this signal level is compared with a reference signal level to determine its value. a gain control circuit that generates a second control signal to bring the difference close to zero and feeds it back to the second variable gain circuit; and a gain variable operation of the first variable gain circuit based on the first control signal. 1. A transmission power control circuit for a wireless communication device, comprising: a variable loop gain circuit that varies a loop gain of the gain control circuit in response to a change in the loop gain of the gain control circuit.