JPH08186456A - Automatic gain controller - Google Patents

Abstract

PURPOSE: To follow up even high-speed received electric field strength fluctuation like fluorescent lamp fading as well. CONSTITUTION: This device is provided with a variable gain circuit 13 for inputting the received signal of a radio communication terminal, electric field strength detecting circuit 14 for outputting electric field strength information by detecting the electric field strength of the received signal, sampling circuit 18 for sampling the electric field strength information in a prescribed sampling cycle, and memory 21 for inputting the sampled electric field strength information and storing information for one cycle in the electric field strength fluctuating components of prescribed cycles at least. Then, gain control circuits 17 and 23 are provided to control the gain of the variable gain circuit 13 based on the information read out of this memory 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic gain control device, and more particularly to an automatic gain control device suitable for a wireless communication terminal used indoors in a wireless LAN or a second generation cordless telephone system.

[0002]

2. Description of the Related Art In a wireless terminal used for mobile communication, the electric field strength of a received signal fluctuates due to movement of the terminal itself or movement of people around the terminal. Therefore, the terminal is usually provided with an automatic gain control (AGC) function in order to set the signal voltage input to the detection unit to an appropriate value and always ensure good communication quality. One of the performances required for such an AGC is the followability to the fluctuation of the received electric field strength. Since the frequency of the received electric field strength fluctuation is generally determined by the moving speed of the terminal and the radio frequency band used, the value varies depending on the situation in which the terminal is used. Generally, the AGC is designed based on the assumed worst value. To be done. The frequency of the received electric field strength variation is, for example, about 6 Hz in the second generation cordless telephone and 50 Hz to 80 Hz in the car telephone.

On the other hand, in a wireless communication terminal used indoors such as a terminal of a cordless telephone, in addition to the fluctuation of the received electric field strength caused by the movement of the above-mentioned terminal and the surrounding people, the electric field received by the fluorescent lamp is further added. There are variations in intensity. Since the fluorescent lamp looks like a conductor to radio waves when turned on and looks like an insulator when turned off, the electric waves entering the fluorescent lamp undergo amplitude modulation at twice the power supply frequency of the commercial AC power supply. For this reason,
Due to the interference between the reflected wave from the fluorescent lamp and the direct wave that does not enter the fluorescent lamp, the electric field strength variation synchronized with the power supply frequency occurs in the received signal. Such a variation in the received electric field strength due to the fluorescent lamp is called fluorescent lamp fading. The fluctuation speed of the received electric field intensity due to the fading of the fluorescent lamp is twice the lighting cycle of the fluorescent lamp, that is, twice the power supply frequency. Specifically, it is 100 Hz in the Kanto area and 120 H in the Kansai area.
z is a high speed compared to z and the speed of fluctuation due to movement of the terminal or movement of people around.

There is no problem if the AGC of the wireless communication terminal can follow such a change in the received electric field strength at a high speed, but the conventional AGC is designed to follow a low speed fading. However, it has been difficult to follow high-speed electric field strength fluctuations such as fluorescent lamp fading.
As a result, with respect to the fading of the fluorescent lamp, the input voltage of the detector after the AGC is not controlled within the predetermined range, which causes a problem that the communication quality deteriorates.

[0005]

As described above, since the AGC built in the conventional wireless communication terminal cannot follow the high-speed fluctuation of the received electric field strength due to the fluorescent lamp, the wireless used indoors. The communication terminal has a problem that the communication quality is deteriorated. It is an object of the present invention to provide an automatic gain control device capable of following a high-speed received electric field strength variation such as fluorescent lamp fading.

[0006]

In order to solve the above-mentioned problems, the present invention focuses on the fact that the fluctuation of the received electric field strength of the received signal due to the fluorescent lamp has a periodicity depending on the power supply frequency. The essence is that the information of the electric field strength variation component is stored and the automatic gain control is performed based on the information.

That is, the automatic gain control device according to the present invention detects the electric field strength of the variable gain means which receives the received signal of the wireless communication terminal and the electric field strength of the received signal, and outputs the electric field strength information at a predetermined sampling period. Sampling means for sampling, storage means for inputting the electric field strength information sampled by the sampling means and storing information for at least one cycle of the electric field strength fluctuation component of a predetermined cycle, and information based on the information read from the storage means And a gain control means for controlling the gain of the variable gain means.

In this case, it is desirable that the sampling cycle of the sampling means is different from the fading cycle of the fluorescent lamp installed indoors where the wireless communication terminal is used. That is, it is desirable that the sampling frequency be a frequency different from an integral multiple of the frequency of the commercial AC power supply. In other words, it is desirable to set the sampling period such that an integer multiple of the difference between the sampling period and the fluorescent lamp fading period is equal to the fluorescent lamp fading period.

Further, another automatic gain control device according to the present invention is a difference detecting means for detecting a difference between the information read from the storage means and the electric field strength information, and an output of the difference detecting means for a predetermined time. It is characterized by further comprising an integrating means for integrating and an updating means for updating the contents of the storage means when the output of the integrating means exceeds a predetermined value.

When the present invention is applied to an automatic gain control device used in a wireless communication terminal used in a time division multiplexing system, the electric field strength information and the sampled information read from the storage means are compared, Phase detection means for outputting a relative phase with respect to a fluorescent lamp fading cycle at sampling points having the same electric field strength, and time tn
The output of the phase detection means detected at (n; integer) is used as an initial value, and the initial value and the information read from the storage means are used as inputs, and at time tn + m (where tn + m> tn,
m; integer greater than or equal to 1), and further comprising an electric field strength estimating means for estimating and outputting the electric field strength expected to be detected.

In this case, the output of the commercial AC power source used as the power source of the wireless communication terminal may be used as the input of the phase detecting means as the information of the period of the fluorescent lamp fading. Also,
In the present invention, a light detecting means for detecting the lighting time and the extinguishing time of the fluorescent lamp may be provided, and the output of the light detecting means may be used as the input of the phase detecting means as information of the cycle of the fluorescent lamp fading.

Further, according to the present invention, a band-pass filter having a cut-off characteristic having a cut-off center frequency that is twice the frequency of a commercial AC power supply used as a power supply for a wireless communication terminal is used to make a fluorescent lamp fading included in a received signal. It is also possible to eliminate the effect of.

[0013]

The cycle of the fluorescent lamp fading, that is, the cycle of fluctuations in the received electric field strength of the wireless communication terminal due to the blinking of the fluorescent lamp is a fixed value that depends on the frequency of the commercial AC power source that drives the fluorescent lamp. The fluctuation of the received electric field strength due to fading of the fluorescent lamp for a sufficiently long time can be regarded as a periodic function of the fading cycle.

According to the present invention, periodical fluctuation information of the received electric field intensity due to fading of a fluorescent lamp or the like is stored in advance, and the received electric field intensity at a predetermined time can be accurately estimated. Therefore, this is used. Automatic gain control.
By doing so, it becomes possible to follow a high-speed received electric field strength fluctuation such as fading of a fluorescent lamp.

Further, the situation of the fluorescent lamp fading changes depending on the person around the wireless communication terminal or the movement of the terminal itself. When the situation of fading of the fluorescent lamp changes in this way, the information stored in the storage means becomes improper because it does not reflect the electric field strength fluctuation due to the actual fading of the fluorescent lamp.

Therefore, in the present invention, the difference between the information read out from the storage means and the electric field strength information obtained in real time by the electric field strength detection means is detected and integrated for a predetermined time, and the integrated value becomes a predetermined value or more. In this way, by updating the contents of the storage means, it is possible to always perform the optimum automatic gain control in response to the change in the fading of the fluorescent lamp.

[0017]

【Example】

(Embodiment 1) FIG. 1 is a block diagram showing the configuration of an automatic gain control device according to an embodiment of the present invention. In the figure, after the received signal received by the antenna 11 is extracted by the band pass filter 12 only the desired frequency component,
It is input to the variable gain circuit 13 and the electric field strength detection circuit 14. The electric field strength detection circuit 14 usually detects the electric field strength of the received signal in the intermediate frequency band or the base band in the wireless terminal. When detecting the electric field strength in the intermediate frequency band, the voltage is generally detected after passing through a filter having a low-pass characteristic. Further, when the electric field strength is detected in the base band, the complex envelope is detected from the I and Q channels after the quadrature demodulation. The present invention can be applied to any of these cases, but detection in a baseband band where it is difficult to increase the response speed is particularly effective.

The difference between the electric field intensity information Et output from the electric field intensity detection circuit 14 and the reference value is obtained by the subtractor 15, and this difference is obtained by the low pass filter 16 and the adder 1.
After that, it is supplied to the variable gain circuit 17 as a gain control signal. The variable gain circuit 17 is composed of, for example, a variable gain amplifier whose gain can be electrically controlled. These electric field strength detection circuit 14-subtractor 15-low pass filter 16
~ Adder 17 ~ The control loop by the variable gain circuit 17 is
Similar to a conventionally provided AGC loop for keeping the amplitude of the signal output from the variable gain circuit 17 constant with respect to a normal received electric field strength fluctuation due to the movement of the wireless communication terminal or the movement of people around. It is a thing.

The electric field intensity information Et output from the electric field intensity detection circuit 14 is A for fluorescent lamp fading.
For the purpose of GC, it is also input to the sampling circuit 18, and the period Ts from the sampling clock generation circuit 19 is input.
Sampling clock is used for sampling. The sampling circuit 12 and the electric field strength detection circuit 1
The order of 4 may be reversed from that of FIG. The sampling clock may be obtained by dividing the clock generated in the wireless communication terminal. Sampling circuit 18
From the sampled discrete electric field strength information Ek
Is output. The electric field strength information Ek is temporarily held in the data register 20.

The data register 20 is composed of, for example, a shift register, and the number of stages thereof is set based on the cycle of the fluorescent lamp fading and the frequency of the sampling clock. For example, the electric field intensity sampled for one cycle of the fluorescent lamp fading Assuming that the information Ek is held, if the difference between the phosphor fading period and the sampling interval is 1/10 of one period of the phosphor fading, 10
It is a step. Assuming that the data length that can be stored in the data register 20 is n (n; integer), the data register 20 stores {e
The electric field strength information of 1, e2, ..., En} is held.

The output of the data register 20 is the memory 21.
Is written under the instruction of the write enable signal WE. The memory 21 can be rewritten from the outside after manufacturing, and a RAM, EPROM, shift register, or the like is used. The contents of the memory 21 are read by the read clock from the read clock generation circuit 22 during communication. An address signal synchronized with the read clock may be used instead of the read clock. Further, although the output of the data register 20 is directly input to the memory 21 in FIG. 1, it may be input via the CPU.

The electric field intensity variation information read from the memory 21 is converted into an analog gain control signal for AGC for fluorescent lamp fading by the D / A converter 23, and then is fed to the variable gain circuit 13 via the adder 17. It is supplied as a gain control signal. When the gain control is performed discretely, the digital electric field strength information read from the memory 21 may be used as it is as the gain control signal without using the D / A converter 23.

Next, the operation of this embodiment will be described with reference to FIG. The fading of the fluorescent lamp, that is, the fluctuation of the received electric field strength due to the fluorescent lamp can be regarded as a function of the period TfL in a sufficiently long time. Here, TfL is the period of fluorescent lamp fading. That is, the fluctuation of the electric field intensity received by the fluorescent lamp is represented by E (t) = E (t−n · TfL) n: an integer, which is represented by a waveform as shown in FIG. The maximum fluctuation level of the electric field intensity due to this fluorescent lamp is generated in each cycle TfL as shown in FIG. In this embodiment, the electric field intensity variation information corresponding to the fading of the fluorescent lamp is stored in the memory 21 for one period of the fading period TfL, which is read out from the memory 21 at any time and reflected in the gain control for the variable gain circuit 13.

Next, a method of estimating the electric field strength variation for one fading cycle by using the electric field strength information sampled by the sampling circuit 18 will be described. The electric field intensity information E (t) shown in FIG. 2A is input from the electric field intensity detection circuit 14 to the sampling circuit 18, and the sampling clock generation circuit 19 outputs an appropriate period Ts (sampling period) shown in FIG. 2B. By sampling with the sampling clock of, the discrete electric field intensity information {e1, e2, e3, ..., E shown in FIG.
6} is obtained. Here, the sampling period Ts is T
By setting s ≠ mTfL (n: integer), it is possible to sample electric field strength information of different phases. By setting the sampling period Ts in this way, it is equivalent to sampling the electric field intensity information for one period by the sampling clock of the period TfL-Ts. This point will be described in detail with reference to FIG.

FIG. 3 shows the relationship between the sampling period Ts, the fluorescent lamp fading period TfL, and the period Ter = TfL-Ts defined by the difference between the two. Although Ts <TfL is set in FIG. 3, Ts> TfL may be set. Here, at the rising edge of the sampling clock shown in FIG.
When sampling the electric field strength information, one sample of the electric field strength information is detected within one cycle of the fluorescent lamp fading, and the detection time is one cycle section of the fluorescent lamp fading, such as Ter → 2 × Ter → 3 × Ter. Then, the time is shifted by Ter. In this case, the fading period (TfL
/ Ter) times, if one cycle period of the fluorescent lamp fading is repeated, it is equal to (TfL / Ter) samples / cycle of the electric field intensity fluctuation due to the fluorescent lamp fading. For example, the fading period TfL is 1/1
00Hz, sampling clock frequency is 11kHz
Then, there are 10 samples per unit period, and the time required to acquire all data is 1 sec.

Thus, by setting the sampling period Ts so that the integral multiple of the difference between the sampling period Ts and the period TfL of the fluorescent lamp fading becomes equal to TfL, the fluorescent lamp fading is shown in FIG. 2 (a). Electric field strength fluctuations can be estimated.

Next, a method of reading the electric field strength variation information stored in the memory 21 and reflecting it in the gain control will be described. Since the sampled electric field strength information is effective for a sufficiently long time, it is used as EPROM or RAM.
Alternatively, the electric field strength can be estimated without performing the integration operation used in the conventional AGC by storing the data in the memory 21 including a latch circuit such as a register and inputting and reading the address data synchronized with the read clock. It is possible. This operation will be described with reference to FIG.

The clock of the period TR shown in FIG. 2E is a read clock for reading the data of the sampled electric field strength information stored in the memory 21, and is generated by the read clock generation circuit 22. . Here, by setting TR = Ter, it becomes possible to estimate the electric field strength fluctuation shown in FIG. 2D due to the fading of the fluorescent lamp. Then, the estimated value of the electric field strength fluctuation read from the memory 21 is synchronized with the received electric field strength fluctuation shown in FIG. 2A and used for gain control of the variable gain circuit 13.

Next, a method for synchronizing the thus-estimated electric field strength fluctuation of FIG. 2D with the received electric field strength information of FIG. 2A will be described. Electric field intensity fluctuations due to fluorescent lamp fading of the received signal input to the wireless communication terminal are synchronized with the lighting cycle of the fluorescent lamp and the commercial AC power supply used by the wireless communication terminal. Therefore, by using the photodetector output for detecting the turn-on time and turn-off time of the fluorescent lamp, and the amplitude information of the commercial AC power source, the fluorescent lamp fading of the received signal input to the wireless communication terminal is detected in any sample value in the memory 21. You can see if it corresponds to. That is, when a photodetector that maximizes the fluorescent lamp fading when the photodetector output reaches the maximum value is used, sampling in the memory 21 is performed in synchronization with the time when the photodetector output reaches the maximum. The maximum value data, that is, e6 in FIG. 2D may be read out from the values. On the other hand, it suffices to detect the amplitude value of the commercial AC power supply and output a predetermined value from the sampling values in the memory 21 in synchronization with the time when the maximum amplitude value is detected.

In the present embodiment, the characteristic that the fluorescent lamp fading is synchronized with the lighting cycle of the fluorescent lamp and the cycle of the commercial AC power source is used, but the electric field corresponding to the fluorescent lamp fading is obtained only from the detected electric field intensity information. It is possible to establish synchronization between the estimated value of the intensity fluctuation and the actual fading of the fluorescent lamp received by the wireless communication terminal. This will be described in detail later.

(Embodiment 2) FIG. 4 shows a main part of an automatic gain control apparatus according to this embodiment. In addition to the configuration of FIG. 1, a means for updating the data stored in the memory 21 is newly added. It is provided in. As described above, the memory 21 stores the electric field intensity variation information due to the fading of the fluorescent lamp for one cycle, but the fading of the fluorescent lamp is accompanied by the movement of the person or the object around the wireless communication terminal or the wireless communication terminal. The state of changes. Therefore, in reality, it is necessary to appropriately update the contents of the memory 21 according to changes in the fading of the fluorescent lamp.

Referring to FIG. 4, the sampling circuit 1 of FIG.
The electric field intensity information Ek sampled in 8 is held in the data register 20. The data register 20 is a shift register, and holds the held data in the sampling circuit 1.
It shifts downward one by one in 8 sampling cycles. The memory 21 reads the data held in the data register 21 by the write enable signal WE. Here, in the present embodiment, the electric field strength information detected by the electric field strength detection circuit 14 of FIG. 1 in real time is compared with the electric field strength fluctuation information output from the memory 21, and the comparison output becomes a certain value or more. Then, the write enable signal WE is output.

That is, the electric field intensity detection circuit 1 output from the difference detection circuit 25 via the data register 20.
4 and the electric field strength variation information from the memory 21 output from the memory 21 via the data register 26 are obtained. The data register 26 is provided to synchronize the two inputs of the difference detection circuit 25. The difference information output from the difference detection circuit 25 is input to the cumulative adder 27 and cumulatively added for a certain period of time, that is, integrated. The output of the cumulative adder 27 is input to the comparator 28 and compared with the predetermined value Vth. The comparator 28 is
When the output of the cumulative adder 27 becomes equal to or higher than the predetermined value Vth, the write enable signal WE is output to the memory 21.

As described above, in the present embodiment, the electric field strength information detected in real time by the electric field strength detection circuit 14 of FIG. 1 is compared with the electric field strength fluctuation information held in the memory 21, and the difference between the two is found. By updating the contents of the memory 21 when the value becomes equal to or more than the predetermined value, it is possible to always perform more appropriate automatic gain control corresponding to the change in the fading of the fluorescent lamp.

(Embodiment 3) In this embodiment, an automatic gain control device incorporated in a radio communication terminal used for time division multiplex communication (TDMA) will be described. In time division multiplex communication, the wireless communication terminal receives at the timing of the frame cycle. When the fluctuation of the electric field strength due to fading is sufficiently long with respect to the length of the time division slot, the electric field strength can be regarded as constant within the slot. Particularly, in the case of AGC in which the gain control is switched not continuously but discretely, noise is generated at the time of switching and the transmission quality is deteriorated. In order to avoid this, it is effective to set the gain in the slot received at time tn + 1 in the unused slot section based on the electric field strength detected in the slot received at time tn.

However, such gain control can be applied only when it is assumed that the electric field strength variation due to fading is sufficiently slow with respect to the slot interval.
Hitherto, it has been difficult to follow high-speed electric field strength fluctuations such as fluorescent lamp fading. For example, the frame frequency of the second-generation cordless telephone is 200 Hz, which is twice the frequency of fluorescent lamp fading (100 Hz) in the Kanto area. That is, the slot is received twice in one cycle of the fluorescent lamp fading, and the gain switching type AG that uses the received electric field strength information detected in the previous reception slot.
In the case of C, the reception quality is predicted to deteriorate due to a gain switching malfunction.

On the other hand, in this embodiment, paying attention to the fact that the time of the slot next received by the wireless communication terminal is known, the fading pattern of the fluorescent lamp which is learned and stored in advance,
By estimating the electric field intensity fluctuation of the fluorescent lamp fading in the next receiving slot from the history of the electric field intensity detected in the past and reflecting it in the gain control, it is possible to avoid the malfunction of the gain switching in advance.

This operation will be described in detail with reference to FIG. FIG. 5A shows a waveform of fluorescent lamp fading that the terminal has previously learned. Here, TfL is the period of fluorescent lamp fading. It is assumed that the learned waveform is valid for a sufficiently long time. When the fluorescent lamp fading occurs as shown in FIG. 5A, the timing of the slot to be received is shown in FIG. 5B as an example. Here, the interval of the receiving slots, that is, the frame period is TsL. The electric field strength detected in each slot is shown by e0 to e4 in FIG. Here, since the frame period TsL and the fading period TfL are constant, the electric field intensities e1 to e4 detected thereafter can be estimated by specifying the position B0 of the first slot as the relative phase with respect to the fading period. Hereinafter, a method for performing phase detection for fluorescent lamp fading in the initial slot will be described in detail.

FIG. 6 describes a method of detecting the phase in the first one slot. Here, the phase is defined as the slot reception time with respect to the fluorescent lamp fading cycle. In the present embodiment, the phase detection is performed by detecting the electric field strength value and the difference value, which is effective when there is some variation in the electric field strength within one slot section. In FIG. 6, the electric field intensity detection circuit 30 detects the average electric field intensity in the slot from the instantaneous value of the electric field intensity. Normally, the integrated value is used in the slot. You may substitute with the integrated value. Here, the average electric field strength of the slot is ei. The other electric field intensity detection circuits 31, 32, 33 output the values eib, eim, eie obtained by integrating the instantaneous electric field intensity for a predetermined time before, during, and after the slot, respectively.

The difference circuits 34 and 35 have a relative strength (eim-eib) at the central portion with respect to the front portion of the slot and a relative strength (ei) at the rear portion with respect to the central portion of the slot.
e-eim) is obtained and both code information (+ or-) is output. Here, when the sign information output from the difference circuits 34 and 35 is positive, it can be determined that the electric field strength has increased in the detection section, and conversely, when the sign information is negative, the electric field strength is in the detection section. Can be determined to have decreased. The difference circuit 3
When 4 and 35 are realized by digital signal processing, the MSB may be substituted for the code information.

The memory 36 estimates and outputs the relative initial phase B0 based on the absolute value of the electric field strength and the code information from the difference circuits 34 and 35. That is, the electric field intensity detected by the electric field intensity detection circuit 30 may have two phases. It is the phase for ei in the monotonically increasing part and the phase for ei in the monotonically decreasing part. In the present embodiment, these distinctions are made by using the difference information of the electric field strengths detected before and after the slot.

Next, a method of identifying the phase of the receiving slot with respect to the fading of the fluorescent lamp based on the history information of the detected electric field strength will be described. In this embodiment, based on the electric field strength information detected in the first slot, a group of candidate values of the electric field strength that can be estimated to be detected in the second slot is determined, and the candidate value group and the electric field strength detected in the second slot are determined. To determine the phase information of the first slot.

This initial phase determination procedure will be described with reference to the flowchart shown in FIG. First, the slot is received at time ti and the electric field strength ei is detected (steps S1 to S).
2). It is assumed that the terminal learns the electric field strength variation with respect to the phase of the fluorescent lamp fading in advance and stores it in the storage table shown in step S3. Therefore, by referring to this storage table, the phase candidates φ1 and φ2 for the electric field strength fluctuation ei can be known. Furthermore,
When the relative phase of slot i is φ1 and φ2,
The absolute value of the electric field strength detected in slot i + 1 can be estimated.

In the next step S4, the estimated values of the electric field strength of the own slot with respect to the initial phase are φ1 → e3 and φ, respectively.
2 → e4. Then, at time ti + 1, slot i +
1 (step S5), and further the electric field strength ei + 1
Of the electric field intensity estimated previously by detecting
+1 is compared (step S6), and if it is e3, it is determined that the initial phase is φ1 (step S7), and if it is e4, it is determined that the initial phase is φ2 (step S).
8). When the error between e3 and e4 is small enough,
It is clear that approximately φ1 = φ2. Furthermore, the difference between the detected electric field intensity ei + 1 and each of the candidate values e3 and e4 may be obtained, and the phase paired with the smaller difference may be used as the initial value. The learning of the electric field strength variation by the fluorescent lamp can be performed by matching the sampling cycle Ts with the frame cycle in the first embodiment.

(Embodiment 4) FIG. 8 is a diagram showing an embodiment in which the frame cycle is an integral multiple of the fluorescent lamp fading cycle, as in the second-generation cordless telephone. In the present embodiment, since the frame period is synchronized with the period, the fact that the same electric field strength sampled in the slot is likely to be repeated is used to perform gain control based on past detection values. The variable gain circuit 41 is controlled to a desired gain by the gain control signal from the gain control table 45. The received signal is amplified by the variable gain circuit 41 to the A / D converter 42 in the subsequent stage so as to have an appropriate voltage value, and then digitized by the A / D converter 42. A
The output of the / D converter 42 is input to the electric field strength detection circuit 43, and the envelope level of the received signal is detected,
The electric field strength information is output.

This electric field strength information is input to the shift register 44, delayed by the clock 46 synchronized with the slot, and output. The delay amount of the shift register 44 is set so that the output electric field intensity and the electric field intensity detected in the gain-controlled slot match.

The received signal actually undergoes slow fading due to movements of people around and movements of the terminal as often described. In order to deal with this, in the present embodiment, the output of the shift register 44 and the electric field intensity detection circuit 4
Difference circuit 47 for obtaining the difference from the electric field strength detected in 3.
The electric field strength variation amount is calculated by, and this is reflected in the gain control by the gain control table 45. The gain control table 45 includes a D / A converter when the gain control is performed by continuous control.

Next, the operation of this embodiment will be described with reference to FIG. FIG. 9A shows a variation in electric field strength in the case where relatively slow fading due to movement of people around the terminal or movement of the terminal itself is further superimposed on fading of the fluorescent lamp having the period TfL. In this embodiment, a wireless terminal is assumed to be applied to a time division multiplex system, and a case will be described in which reception is performed in a burst at every cycle TsL. For example, in the second-generation cordless telephone, 1 / TsL = 200 Hz, as shown in FIG.
As shown in (b), burst reception is performed twice per one period section of fluorescent lamp fading. FIG. 9C shows the received electric field strength value E (k) detected in each received burst. Here, the transition 50 of the electric field strength detection value between consecutive bursts
On the other hand, the level fluctuations between bursts are smaller in the field intensity transitions 51 and 52 detected every other. Since the burst length is sufficiently shorter in time than the fading cycle, the gain setting need only be made once within the burst.

That is, when slow fading is assumed, it is possible to set the next gain based on the electric field strength information detected in the reception slot two times before. This is generally the fluorescent light fading period TfL and T
This is effective when the relationship of the DMA frame period TsL is an integral multiple. That is, when TfL = m · TsL (m; integer), the electric field strength information detected before m bursts may be referred to.

(Embodiment 5) Actually, the storage table (e, φ) shown in FIG. 7 is periodically updated due to the synchronization error between the frame period TsL and the fading period TfL and the change in the usage condition of the terminal. is necessary. Therefore, in the present embodiment, an automatic gain control device provided with this storage table (e, φ) updating means will be described.

In FIG. 10, the gain of the variable gain circuit 60 is controlled by the control signal from the gain estimator 61. The storage table 62 stores the electric field intensity e that has been learned and stored in advance.
And a table (e, φ) corresponding to the relative phase φ, with the initial electric field strength e0 and the slot reception time ti as inputs,
History of these and past electric field strengths {e0, e1, ..., e
i-1} and the electric field strength received at a predetermined time ti are predicted and output to the synchronization circuit 65. The subtracter 63 is an actual value obtained by the electric field strength detection circuit 63 from the estimated value of the received electric field strength input via the synchronization circuit 65 and the received signal amplified by the variable gain circuit 60 having a gain set based on the estimated value. The error from the electric field strength of is calculated. Then, the integrating circuit 66 outputs a value 67 obtained by integrating the error output from the subtractor 65 for a certain period of time, and using this, the table 62 is updated.

(Embodiment 6) FIG. 11 shows an automatic gain control device according to this embodiment. Normally, the fluorescent lamp fading cycle is sufficiently faster than the fading cycle due to movement of a person or surroundings, and thus the first embodiment has two AGCs corresponding to these different fading cycles.

On the other hand, in the present embodiment, the fact that the fading period of the fluorescent lamp is known in advance is utilized, as shown in FIG.
By using a band stop filter having a characteristic having a stop band at the fluorescent lamp fading frequency TfL as shown in the figure, the influence of the fluorescent lamp fading is eliminated to simplify the AGC configuration.

Specifically, in this embodiment, after the output signal of the variable gain circuit 70 is digitized by the A / D converter 75, the envelope detection circuit 74 digitally detects the envelope level, and The fluctuation is detected. Here, the envelope level fluctuation is detected by the envelope detection circuit 74, the difference circuit 73 that takes the difference between the output of the envelope detection circuit 74 and the reference value, the loop filter 72 and the loop gain for noise suppression. This is performed by the application circuit 71. Here, the loop gain given by the loop gain giving circuit 71 is set on the basis of a time constant in consideration of movements of a person or surroundings. In this embodiment, the AGC is a feedback loop, but it may be a feedforward loop.

On the other hand, the band stop filter 76 having the band stop characteristic in the period of the fluorescent lamp fading is added to the A / D converter 75.
By arranging on the output side of, the electric field strength fluctuation due to high speed fading is absorbed. This operation will be described with reference to FIG.

FIG. 12A shows the received signal waveform Ein affected by the fading of the fluorescent lamp. As shown in the figure, the electric field strength greatly decreases in each cycle TfL. The magnitude of the received signal Ein affected by the fading of the fluorescent lamp is usually as large as 20 to 30 dB under the condition that the direct wave is weakened by the interference, but is about 10 dB in most cases. Further, since the period in which the electric field strength drops is constant, as shown in FIG. 12C, the band cutoff filter 76 having a cutoff center frequency is passed through 1 / TfL as shown in FIG. In addition, it is possible to weaken the influence of electric field strength fluctuation. The output of the band cutoff filter 76 may be used as the input of the envelope detection circuit 74.

[0057]

As described above, according to the present invention, the fluctuation of the electric field strength due to the fading of the fluorescent lamp has a periodicity, that is, the fading frequency is twice the commercial AC power supply frequency, and the fading of the fluorescent lamp is suppressed. Focusing on the fact that the level of electric field strength fluctuations is almost constant over a sufficiently long time compared to the movements of people and wireless terminals in the surroundings, the information of fluctuations in the received electric field strength for a predetermined period due to fluorescent lamp fading is sampled and stored. By reading this and performing automatic gain control, it is possible to provide an automatic gain control device with a simple configuration and capable of following changes in electric field strength due to high-speed fluorescent lamp fading.

Further, by integrating the difference between the stored electric field strength variation information and the electric field strength information detected in real time, and updating the stored contents when the integrated value exceeds a predetermined value, the wireless communication terminal It is possible to always perform optimum automatic gain control in response to changes in the status of fluorescent lamp fading due to movement of people around the terminal or the terminal itself.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an automatic gain control device according to a first embodiment of the present invention.

FIG. 2 is a timing chart for explaining the operation of the first embodiment.

FIG. 3 is a timing diagram of a sampling clock for explaining the operation of the first embodiment.

FIG. 4 is a block diagram showing a configuration of a main part of an automatic gain control device according to a second embodiment of the present invention.

FIG. 5 is a timing diagram for explaining an automatic gain control device according to a third embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of a main part of an automatic gain control device according to a third embodiment.

FIG. 7 is a flowchart illustrating an initial phase determination procedure according to the third embodiment.

FIG. 8 is a block diagram showing a configuration of a main part of an automatic gain control device according to a fourth embodiment of the present invention.

FIG. 9 is a timing chart for explaining the operation of the fourth embodiment.

FIG. 10 is a block diagram showing a configuration of a main part of an automatic gain control device according to a fifth embodiment of the present invention.

FIG. 11 is a block diagram showing a configuration of a main part of an automatic gain control device according to a sixth embodiment of the present invention.

FIG. 12 is a diagram for explaining the operation of the sixth embodiment.

[Explanation of symbols]

 11 ... Antenna 12 ... Filter 13 ... Variable gain circuit 14 ... Electric field intensity detection circuit 15 ... Subtractor 16 ... Low-pass filter 17 ... Adder 18 ... Sampling circuit 19 ... Sampling clock generation circuit 20 ... Data register 21 ... Memory 22 ... Read clock Generation circuit 23 ... D / A converter 24 ... Gain control signal 25 ... Difference detection circuit 26 ... Data register 27 ... Cumulative adder 28 ... Comparator 30-33 ... Electric field intensity detection circuit 34 ..., 35 ... Difference circuit 36 ... Memory 41 ... Variable gain circuit 42 ... A / D converter 43 ... Electric field intensity detection circuit 44 ... Shift register 45 ... Gain control table 46 ... Clock 47 ... Subtractor 60 ... Variable gain circuit 61 ... Gain estimation unit 62 ... Storage table 63 ... Electric field strength detection circuit 64 ... Subtractor 65 ... Synchronization circuit 66 ... Integration circuit 67 ... Min value 70 ... variable gain circuit 71 ... loop gain applying circuit 72 ... loop filter 73 ... subtractor 74 ... envelope detection circuit 75 ... A / D converter 76 ... notch filter

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuo Suzuki 1 Komukai Toshiba-cho, Kouki-ku, Kawasaki-shi, Kanagawa Ltd. Inside Toshiba Research and Development Center

Claims (2)

[Claims] 1. A variable gain means for receiving a received signal of a wireless communication terminal, a sampling means for detecting an electric field strength of the received signal and sampling the electric field strength information at a predetermined sampling period, and the sampling means. Storage means for inputting the sampled electric field strength information and storing information for at least one cycle of the electric field strength fluctuation component of a predetermined cycle, and the gain of the variable gain means is controlled based on the information read from this storage means. An automatic gain control device comprising: a gain control means. 2. A variable gain means for receiving a received signal of a wireless communication terminal, a sampling means for detecting an electric field strength of the received signal and sampling the electric field strength information at a predetermined sampling period, and the sampling means. Storage means for inputting the sampled electric field strength information and storing information for at least one cycle of the electric field strength fluctuation component of a predetermined cycle; and a difference for detecting a difference between the information read from the storage means and the electric field strength information. Detecting means, integrating means for integrating the output of the difference detecting means for a predetermined time, updating means for updating the contents of the storing means when the output of the integrating means exceeds a predetermined value, and read from the storing means An automatic gain control device comprising: a gain control means for controlling the gain of the variable gain means based on information.