FR2782583A1 - SIGNAL PROCESSING UNIT - Google Patents

Abstract

A signal processing unit includes a first gain control block (20) for controlling the gain of an input signal (50), a signal processing block (10) disposed in the stage placed after the gain control block, and an energy detection block (30) for detecting the energy of the output signal of the signal processing block and controlling the amplitude of variation of gain of the gain control block in depending on the amount of energy detected. The first gain control block (20) compresses the amplitude of the input signal to a level corresponding to the dynamic range of the signal processing block, and supplies the compressed signal to the signal processing block. Therefore, even in the case where the dynamic range of the signal processing block is small, a large dynamic range can be provided for the unit as a whole.

Description

The present invention relates to a signal processing unit

  for processing received signals and, more specifically, a signal processing unit having an automatic gain control circuit (hereinafter referred to

  AGC circuit) for integration into a large scale integrated circuit, or LSI.

  An AGC circuit is used to detect the intensity of a received signal (input signal) and to form an output signal by compressing the amplitude of the received signal to a predetermined degree, or smaller. Various forms of AGC circuits are known. By way of example of a signal processing unit comprising a similar AGC circuit, FIG. 1 shows a receiver used in connection with a

  mobile phone. In FIG. 1, the reference numeral 1 denotes a pass filter

  tape, the number 2 a gain control block, and the number 3 a block of

energy detection.

  In this unit, the signal input from an input terminal 5 is applied to the band-pass filter 1, in which the out-of-band noise is eliminated, after which the gain is adjusted, so that it is produced one. appropriate amplitude signal, by an AGC circuit 4 having a gain control block 2 and a power detection block 3. The signal whose gain has been adjusted in the indicated manner is applied via an output terminal 6 , to a demodulation circuit (not shown) for example, in which the desired information

are extracted.

  A prerequisite for the unit of Figure 1 is to use a bandpass filter 1 which is in the stage preceding the gain control block 2 and which therefore requires a large dynamic range. This signal processing circuit is described for example in FIG.

  Japanese Unexamined Patent No. 6-196,954.

  So far, the bandpass filter used was a part external to the LSI.

  A recent trend, however, is to integrate various external parts of the LSI to reduce the cost and bulk of electronic equipment. In particular, there is a strong demand for congestion reduction for mobile phones and, therefore, it is an urgent necessity to integrate the

bandpass filter in the LSI.

  Attempts to integrate the bandpass filter into the LSI, however, require the use of an active circuit employing an amplifier, or the like, in place of the passive circuit used in the prior art, and this reduces the dynamic range in comparison with the prior art o the bandpass filter is an external part. The need is therefore to achieve a signal processing unit which, despite the small dynamic range of the bandpass filter, can ensure, on a unit basis as a whole, a great deal of

dynamic range.

  It is therefore an object of the invention to provide a signal processing unit which can provide a large dynamic range to the unit as a whole, despite the use of a bandpass filter which has a small dynamic range. . Another object of the invention is to produce a signal processing unit that can be built in an LSI without this diminishing the possibilities.

to process the signals.

  Another object of the invention is to produce a portable telephone receiver that is convenient to carry and has a good processing capacity of

  signals, by means of the signal processing unit mentioned above.

  According to the invention there is provided a signal processing unit which comprises a first gain control block for controlling the gain of an input signal, a signal processing block placed in a stage coming after the block. gain control circuit, and an energy detection block for detecting the energy of the output signal of the signal processing block and for automatically adjusting the gain variation of the gain control block as a function of

  the magnitude of the energy detected.

  This signal processing unit is incorporated in the LSI.

  In addition, this signal processing unit is incorporated in the

  receiver and constitutes the receiving unit of a portable telephone.

  In the signal processing unit according to the invention, the dynamic range of the input signal, before it is inputted to the signal processing block, is compressed by the gain control block up to a level adapted to the dynamic range of the signal processing block. Therefore, even when the signal processing block has a small dynamic range, it can be ensured, for the unit as a whole, a large dynamic range. In addition, the automatic gain control is effected by detecting the energy of the output signal of the signal processing block, and therefore, no spurious noise is included in the signal subject to the gain control. As a result, it is possible to precisely adjust the gain of

the wave of the signal to be processed.

  Furthermore, in the signal processing unit according to the invention, the unit as a whole can be provided with a large dynamic range even if the dynamic range of the signal processing block itself is small. Therefore, the signal processing unit can be configured as a circuit

  active and be incorporated into the LSI.

  In addition, it is possible to make a small portable telephone having a high signal processing capability by incorporating this unit of

  signal processing in the receiver of the portable telephone.

  The following description, designed as an illustration of the invention, aims to

  to give a better understanding of its features and benefits; it is based on the appended drawings, among which: FIG. 1 is a block diagram showing a conventional signal processing unit comprising an AGC circuit; Fig. 2 is a block diagram showing a signal processing unit having an improved configuration for integrating the unit of Fig. 1 into an LSI; Fig. 3 is a block diagram showing the basic configuration of a signal processing unit according to the invention; Fig. 4 is a block diagram showing a signal processing unit according to a first embodiment of the invention; Fig. 5 is a diagram for explaining the operation of the unit shown in Fig. 4; Fig. 6 is a flowchart for explaining the operation of the unit shown in Fig. 4; Fig. 7 is a timing chart for explaining the operation of the unit shown in Fig. 4; Fig. 8 is a diagram showing the circuit configuration of the energy detection block according to a second embodiment of the invention; Fig. 9 is a state transition diagram for explaining the operation of the circuit shown in Fig. 8; Fig. 10A is a diagram showing the relationship between each state shown in Fig. 9 and the selection operation performed by a selector; FIG. 1BB is a diagram showing the relationship between the output signals Di, Do shown in FIG. 8 and the gain variation amplitude; Fig. 11 is a diagram showing an LSI in which a plurality of signal processing units of Fig. 3 are incorporated so as to be cascade connected with each other; and Fig. 12 is a diagram showing a signal processing unit according to the invention, which is incorporated in the receiver of a portable telephone. Before describing the embodiment of the invention, the prior art and the drawbacks that it brings about will be explained with reference to FIG. 2. First, it should be noted that the configuration shown in FIG. be considered as a signal processing unit that can ensure a broad overall dynamic range despite the fact that a bandpass filter has a

small dynamic range.

  The particularity of the unit shown in FIG. 2 is to have a configuration in which a bandpass filter 1 is placed in the stage following an AGC circuit 4 comprising a gain control block 2 and a detection block 3. In this unit, placing the AGC circuit 4 in the stage preceding the bandpass filter 1 allows the dynamic range of the input signal to be compressed to the degree appropriate to the dynamic range of the filter. bandpass filter 1 before being applied to the bandpass filter 1. Therefore, even if the dynamic range of the bandpass filter 1 is small, it can be ensured that

  dynamic range for the unit as a whole.

  With the signal processing unit having the configuration shown in Fig. 2, in the case where the input signal contains spurious noise, the AGC circuit 4 adjusts the gain with the spurious noise. As a result, there is interference between the desired wave to be produced at the output of the bandpass filter 1 during gain control and the spurious noise, which leads to a serious problem in

  what the desired waveform is distorted.

  For example, a PDC telephone (personal digital cellular phone) uses frequencies at 25 kHz intervals. However, the receiver only receives one frequency and converts it into an audio signal. All other signals at 25 kHz intervals are treated as noise. The

  The result often obtained is that the parasitic noise is larger than the desired wave.

  The bandpass filter is intended to attenuate the parasitic noise contained in the input signal and to produce only the desired wave. In the receiver which has the configuration shown in FIG. 2, the AGC circuit 4 containing the gain control block 2 and the energy detection block 3 is placed in the stage preceding the bandpass filter 1, and by therefore, it is possible to subject the input wave containing spurious noise to the gain control

performed by the AGC 4 circuit.

  Therefore, depending on the frequency of each interference, the spurious noise may interfere with each other and create intermodulation distortion in the desired waveband. Spurious noise at 550 kHz and 650 kHz, for example, can interfere with each other and create unwanted noise at 450 kHz. This interference combines with the desired 450 kHz waveform to produce signal distortion. This distortion is in the bandwidth and can not

  therefore not be eliminated by the bandpass filter 1.

  As described above, placing an AGC circuit in the stage preceding a signal processing block as a bandpass filter creates a signal distortion that can not be eliminated by the signal processing block in a signal processing block. the next stage, so that a remarkable decrease in

  signal processing capabilities of the unit.

  Fig. 3 is a block diagram showing the basic configuration of the invention. As shown in FIG. 3, the particularity of the unit according to the invention is that a signal processing block 10 consisting of an active band-pass filter for example interposed between a gain control block 20, as an electronic volume control device, and an energy detection block 30. The number 50 designates an input terminal of the received signal, and the number

  an output terminal. These circuits are incorporated in a single LSI 100.

  The signal processing block 10, which is incorporated in the LSI, consists of an active-type bandpass filter or a low-pass filter which, if incorporated in the LSI, necessarily has a range. reduced dynamic compared to external versions. A high-pass filter can also be used. As described above, the unit according to the invention has a configuration feature in that the signal processing block 10 interposes between the gain control block 20 and the detection block.

of energy 30.

  As a result, the energy detection block 30 detects the amplitude of the signal after it has been processed by the signal processing block 10, and controls the gain control block 20 placed in the preceding stage. signal processing block 10, so as to control the gain of the detected signal wave. Therefore, the signal whose gain is adjusted automatically is not affected

  through noise and does not create intermodulation distortion.

  As a result of what has just been stated above, even in the case where an incorporated bandpass filter having a smaller dynamic range than an external version is used as a signal processing block, the automatic control of gain leading to a predetermined amplitude is possible without deformation of the desired wave signal and at the same time

  a great dynamic range for the unit as a whole.

  Fig. 4 is a block diagram showing the configuration of a signal processing unit according to a first embodiment of the invention, which can conveniently be used with the receiver of a portable telephone for example. In FIG. 4, the numbers 21 and 22 respectively designate first and second electronic volume control devices which are controlled by a digital code, the number 11 designates an incorporated bandpass filter, the number 31 designates a detection circuit of energy, and the number 70 designates a demodulation circuit. The numbers 50 and 60 'respectively denote input and output terminals. The component elements 21, 11,

  22, 31 and 70 are incorporated in a single LSI 101.

  The energy detection circuit 31 comprises two comparators 32 and 33 having respectively different reference values VRH and VRL, as well as a logic circuit 34. The energy detection circuit 31 may be of the type

  for detecting the peak value of the signal to be detected, for example.

  Figure 5 shows how the reference value VRH or VRL is selected, depending on the amplitude of the input signal. As can be seen in FIG. 5, the reference value VRH is set at a level such that, if this level is exceeded by the amplitude of the input signal, the gain is reduced by the control circuit automatic gain. Conversely, the reference value VRL is set at a level such that, if this level is greater than the amplitude of the input signal, the gain is increased by the control circuit

automatic gain.

  The amplitude of an input signal between the reference value VRH and the reference value VRL is considered to be within a

  appropriate interval, and the gain is not changed.

  The logic circuit 34 determines where is placed the amplitude level of the signals delivered by the comparators 32 and 33 with respect to the reference values VRH and VRL. The signals indicating the determination made are delivered to the electronic volume control devices 21 and 22. The gain of the electronic volume control devices 21 and 22 is adjusted as presented.

  in FIG. 5, based on the output signal of the logic circuit 34.

  According to this embodiment, the first and second electronic volume control devices 21 and 22 are respectively inserted before and after the bandpass filter 11. In general, the bandpass filter 11 has a significant delay. Thus, it is necessary that the electronic volume control device 12 placed in the stage preceding the bandpass filter 1 1 1 is controlled in a delayed manner to prevent oscillation. The second electronic volume control device 22, which is placed in the floor

  after the bandpass filter, need not be delayed.

  In this manner, the gain control processing is repeated at a high rate between the energy detection circuit 31 and the second electronic volume control device 22, and an integrated value of the control variables is calculated and returned in response. on the first electronic volume control device 21, so that it is possible to control its gain. Thus, gain control processing is possible at the same time

  that the effect of the delay occurring in the bandpass filter 11 is minimized.

  The electronic circuit 34 of the unit shown in FIG. 4 comprises a timer and a circuit for calculating the integrated value of the control variables of the second electronic volume control device 22, as well as a circuit for comparing the calculated value. with a preset convergence value of the gain of the electronic volume control device 22 and outputting a signal for controlling the gain of the first electronic volume control device 21 based on the difference. Such a circuit can be

  configured by appropriate programming of an electronic circuit.

  Fig. 6 is a simplified flowchart showing the operation of the electronic circuit. As shown in FIG. 6, in the first control phase Si, the gain of the electronic volume control device 22 is automatically controlled between the energy detection circuit 31 and the second electronic volume control device 22 in order to providing a constant amplitude to the output signal of the electronic volume control device 22. The convergence value of the gain of the second electronic volume control device 22 is prefixed to CGE. Moreover, the gain of the first

  electronic volume control device 21 is suitably attached.

  Then, in the second control phase S2, the automatic gain control is repeated N times between the energy detection circuit 31 and the second electronic volume control device 22, and a mean gain Ga, is determined. In other words, GV = (Gi + G2 + ... GN) / N is calculated, where G1, G2, ... GCN are the gains of the respective sessions of the automatic control.

  gain made in the electronic volume control device 22.

  Then, in the control phase S3, the value Gv thus obtained is compared with the convergence value GCE of the gain of the second electronic volume control device 22, this operation being followed by the

processes listed below.

  1) In the case where G, is smaller than GE (GV <GE), the gain of

  first electronic volume control device 21 undergoes a decrease.

  Since the amplitude of the input signal of the bandpass filter 11 is correct when G., = G, the fact that the value G., V is smaller than GE indicates that the gain control has caused the latter to descend. between the second electronic volume control device 22 and the energy detection circuit 31, i.e.

  the amplitude of the signal applied to the input terminal 50 was excessively large.

  As a result, the gain of the first electronic volume control device 21 is decreased so that the output signal of the bandpass filter 11

  converges to a predetermined value with a higher speed.

  2) In the case where G.v = GE, the gain of the first electronic volume control device 21 is, on the contrary, not changed. In these conditions,

  the amplitude of the input signal is considered to be in the correct range.

  3) In the case where G.v is larger than GB (G.,> GB), the gain of the first electronic volume control device 21 is increased. Since the input amplitude of the bandpass filter 11 is correct when G. = GC, the situation for which the gain G is greater than the gain GE indicates that the gain has been increased by the automatic control circuit gain device consisting of the second electronic volume control device 22 and the energy detection circuit 31, i.e. the amplitude of the input signal is excessively small, so that the gain of the first device electronic volume control 21 is subjected to an increase, so that the output signal of the bandpass filter 1 can reach a value more quickly

of predetermined amplitude.

  FIG. 7 is a timing diagram showing respectively the first, second and third control sessions SI1, S2 and S3, in the case

o N is 5.

  As described above, the gain is controlled more rapidly by the second electronic volume control device 22, and the average value of the control variables is returned in response to the first volume control electronic device 21 so as to control its gain. As a result, the gain of the input signal can be adjusted more efficiently and more quickly at the same time as avoiding the problem that would otherwise have arisen, namely

  delayed operation of the bandpass filter.

  Fig. 8 is a diagram showing a circuit of the energy detection block 30 of Fig. 3 according to another embodiment of the invention, while Fig. 9 is a state transition diagram for explaining the

  operation of the circuit of Figure 8.

  In this embodiment, the gain variation amplitude in the energy detection block 300 is binary (Ga, Gb, {Ga |> I Gb 1), and the variation amplitude of the gain relating to the block The gain control circuit 20 can be modified according to the quantity detected in the energy detection block 300. The configuration and operation of the circuit will now be explained in connection with FIG. 9 and FIGS. shown in Fig. 8. First, in the circuit of this embodiment, four threshold levels V1, V2, V3 and V4 (V2> V2> V3> V4) are set for the input signal SG, as shown in Fig. 8. Each threshold level is suitably selected by a selector 35 and is applied to the reference input terminals (-) of first and second comparators 36 and 37. The signal input terminals ( +) Comparators 36 and 37 receive, via a band-pass filter 10, a signal denoted IN. Numbers 38 and 39 denote holding circuits which control the output signals of the comparators 36 and 37 for a predetermined time and, only when their output signal goes to 1, maintain the value. The output signals Di and Do of the holding circuits 38 and 39 are applied to a logic circuit 340. It is noted that the holding circuits 38 and 39 receive

  respectively a clock signal CLK, as well as the logic circuit 340.

  The relation existing between the states A, B and C in the state transition diagram of FIG. 9 and the conditions selected from the threshold levels VI, V2, V3 and V4 by the selector 35 is presented in FIG. at). Moreover, the combination of 1 and 0 of the output signals D 1 and C 2 of the holding circuits 38, 39, the amplitude of the input signal determined by this combination, and the gain variation amplitude corresponding to this condition are shown in Figure (b). When the signal input terminals of the comparators 36 and 37 are connected with the threshold levels V3 and V4 via the selector 35 of the circuit of FIG. 9, that is to say that the state A is selected, the Both signals D1 and D1 become null as long as the amplitude of the signal applied to the input of the energy detection block 30 is lower than the threshold level V4. Therefore, on the basis of the decision shown in Fig. 10 (b), the logic circuit 340 determines that the amplitude of the input signal is "lower" than the state A, so that the gain is increased of a gain variation amplitude Ga and that the amplitude of the signal undergoes

a raise.

  In the case where the amplitude of the signal applied to the input of the energy detection block 30 is not lower than the threshold level V4 and is lower than V3, then Di is 0 and Do is 1. On the Based on the decision shown in Fig. 10 (b), the logic circuit 340 determines that the amplitude of the input signal is "intermediate" between state A and state B. In this case, the gain changes by the setting of the gain variation amplitude at + Gb (<Ga) while there is a change of state, which goes from A to B, by modifying the threshold level, aiming at satisfying the state B In addition, in the case where the amplitude of the signal applied to the input of the energy detection block 30 is not lower than the threshold level V3, then the gain does not vary (the amplitude of variation is null), but only the threshold level varies to change from state A to state B. In state B as well as in state C, the state and the gain change according to the transition diagram d estab t in Figure 9 and the decision in Figure (b). Once the state and the gain have changed, the circuit 340 repositioned to "0"

the holding circuits 38 and 39.

  As described above, efficient gain control becomes possible by appropriate selection of the gain variation amplitude of two types, large and small, depending on the amount detected in the sensing block

of energy 30.

  In actual applications of the signal processing unit 100a according to the invention which has the basic configuration of FIG. 3, as shown in FIG. 11, the cascaded units can be connected in a plurality of manner. of these units, and these can be incorporated into a single LSI 100. In addition, as shown in FIG. 12, a small-sized portable telephone can be realized by incorporating the signal processing unit 100 according to the invention in the receiver 110 of the portable telephone, in the form of a single LSI. As described in connection with the embodiments presented above, according to the invention, there is provided a signal processing unit having an automatic gain control circuit, wherein a gain control block is disposed in the stage preceding the signal processing block, and the detected signal gain provided by the output terminal of the signal processing block is adjusted. In the signal subjected to the automatic gain control, the parasitic noise contained in the input wave is thus attenuated sufficiently. As a result, contrary to what happens in the conventional signal processing unit having a signal processing block which is placed in the stage following an automatic gain control circuit, the signal distortion resulting from the existence of a parasitic noise is not found in the signal to be processed. Moreover, in view of the fact that the signal processing block interposes between the gain control block and the energy detection block, the unit as a whole can be provided with a large dynamic range, even if the dynamic range of the signal processing block is small. Therefore, the unit according to the invention operates very efficiently when it is incorporated in a large scale integrated circuit.

  Of course, those skilled in the art will be able to imagine, from

  units whose description has just been given for illustrative purposes only and

  in no way limiting, various variants and modifications not departing from the scope of the invention.

Claims (21)

  A signal processing unit, characterized by comprising: a first gain control block (20; 21) for controlling the gain of an input signal; a signal processing block (10; 11) disposed in the stage placed after said gain control block; and an energy detection block (30; 31) for determining the energy of the output signal of said signal processing block and for automatically controlling the gain variation amplitude of said   gain control block according to the amount of energy detected.   Signal processing unit according to claim 1, characterized in that said signal processing block (10; 11) is selected from a group   comprising a band-pass filter, a low-pass filter and a high-pass filter.   3. signal processing unit according to claim 1, characterized in that a second gain control block (22) interposed between said block of   signal processing (11) and said energy detection block (31).   4. signal processing unit according to claim 2, characterized in that a second gain control block (22) is interposed between said block of   signal processing (11) and said energy detection block (31).   The signal processing unit according to claim 3, characterized in that said energy detection block (31) controls the gain variation amplitude of said first gain control block (21) as a function of the value of d calculated integration of the control variables of the second control block of gain (22).   6. Signal processing unit according to claim 4, characterized in that the integration value of said control variables is calculated by averaging the control variables in several sessions.   gain control of said second gain control block (22).   Signal processing unit according to claim 1, characterized in that said first gain control block (20; 21) is a device   electronic volume control which is controlled by a numerical code.   Signal processing unit according to claim 2, characterized in that said first gain control block (20; 21) is a device   electronic volume control which is controlled by a numerical code.   Signal processing unit according to claim 3, characterized in that at least one of said first and second gain control blocks (21, 22) is an electronic volume control device (21, 22) which is controlled by a numerical code.   The signal processing unit according to claim 1, characterized in that said energy detection block (30; 31) controls the gain of said first gain control block (21) by selecting one of the minus two amplitudes of gain variation as a function of the amplitude level of the signal   outputting said signal processing signal (10; 11).   Signal processing unit according to claim 2, characterized in that said energy detection block (30; 31) controls the gain of said first gain control block (21) by selecting one of the minus two amplitudes of gain variation as a function of the amplitude level of the signal   outputting said signal processing signal (10; 11).   Signal processing unit according to claim 3, characterized in that said energy detection block (31) controls the gains of said first and second gain control blocks (21, 22) by selecting one of said at least two amplitudes of gain variation depending on the level   amplitude of the output signal of said signal processing block (11).   The signal processing unit according to claim 1, characterized in that said energy detection block (30; 31) controls the gain of said first gain control block (21) by determining the peak value of the   output signal of said signal processing block (10; 11).   A signal processing unit according to claim 2, characterized in that said energy detection block (30; 31) controls the gain of said first gain control block (21) by determining the peak value of the   output signal of said signal processing block (10; 11).   Signal processing unit according to claim 3, characterized in that said energy detection block (31) controls the gains of said first and second gain control blocks (21, 22) by detecting the   peak value of the output signal of said signal processing block (11).   Signal processing unit according to claim 1, characterized in that said first gain control block (21), said signal processing block (10; 11) and said energy detection block (30; ) are   arranged in cascade in a plurality of stages (100a).   The signal processing unit according to claim 2, characterized in that said first gain control block (21), said signal processing block (10; 11) and said energy detection block (30; ) are   arranged in cascade in a plurality of stages (100a).   18. Signal processing unit according to claim 1, characterized in that said first gain control block (20; 21), said signal processing block (10; 1 1) and said energy detection block ( 30; 31) are   incorporated into a single large scale integrated circuit, or LSI, (100).   19. Signal processing unit according to claim 3, characterized in that said first and second gain control blocks (21, 22), said signal processing block (11) and said energy detection block.   (31) are incorporated into a single large scale integrated circuit, or LSI, (100).   20. Receiver (110) of a portable telephone, characterized in that it comprises: a signal processing unit (100) having a first gain control block (20; 21) for controlling the gain of a an input signal, a signal processing block (10; 11) disposed in the stage placed after said gain control block, and an energy detection block (30; 31) for determining the energy of the an output signal of said signal processing block and automatically controlling the gain variation amplitude of said gain control block according to the amount of energy detected; and a demodulation circuit (70) for demodulating the output signal   of said signal processing unit.   Receiver of a portable telephone according to claim 20, characterized in that said signal processing block (10; 11) is selected from   a group comprising a band pass filter, a low pass filter and a pass filter. above.