JP2003152593A - Transmission peak limiting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To set the level of a transmission signal to a required limiting amplitude range, without making the quality lowered. SOLUTION: The IQ signal of the base band of an input code sequence is delayed by a delay unit 1, is amplitude-limited by a signal amplitude limiter, then band-limited by a digital LPF 3, converted into an analog signal by a D/A converter 4, and supplied to an orthogonal modulator (not shown) and a transmission amplifier. A filter overshoot estimating unit 5 estimates the extent of the overshoot occuring at the LPF 3 at each code input from an input terminal 6, according to the calculation similar to that of the LPF 3 and the amplitude limit set value, sets an amplitude set value α (<=1) in response to the estimated result, and supplies the set value to a signal amplitude limiter 2. In the limiter 2 the supplied value α is multiplied by the corresponding code, to limit the amplitude for the code which brings about overshooting in the LPF 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission peak limiting circuit for limiting a peak level of a transmission signal generated according to a transmission characteristic in CDMA wireless communication or the like.

[0002]

2. Description of the Related Art In the transmission characteristic of a radio transmission signal, a transmission peak sometimes becomes a problem. For example, CDMA (Co
In a repeater for wireless communication, since the transmission signal is a code multiplex signal, when the received code phase components match, a sudden rise in level (peak level) occurs and Therefore, there arises such a problem that a quadrature modulator or a transmission amplifier for that causes adverse effects such as generation of higher-order distortion.

In order to prevent such distortion, a linear amplifier with extremely low efficiency is required.
Since such an amplifier requires a power consumption that is an order of magnitude higher than that of the transmission amplifier, there is a problem in that the power consumption is significantly increased. Therefore, limiting the transmission peak is an important issue.

Conventionally, in order to limit such a transmission peak, a method of subtly adjusting the modulation phase so that the modulation phases of the respective signals do not match has been adopted, but the structure becomes complicated, but There is a problem that the effect of reducing the peak level is small.

As another method, a peak suppressing signal is dedicatedly provided in advance in the direction of suppressing a transmission peak generated in a composite signal of a plurality of signals, and when a peak occurs, the phase of the peak suppressing signal is increased. There is a method of controlling the peaks so as to be in a phase opposite to the peak phase and limiting the peaks by this, but this also has a problem that the configuration becomes complicated as in the above example.

A simpler method than the above example is to use a limiter that uniquely limits the peak level when it exceeds a required level. FIG. 5 is a block diagram showing an example of a conventional peak limiting circuit showing such a method. Here, a method of performing a limiter operation in a baseband band is taken as an example, where 21 is a signal amplitude limiting section and 22 is a tapped one. Is a digital LPF (low pass filter), and 23 is a D / A (digital / analog) converter.

In FIG. 1, a baseband IQ signal is processed by a signal amplitude limiting section 21 and then a digital LP signal is generated.
The band is limited by F22, converted into an analog signal by the D / A converter 23, and supplied to a quadrature modulation circuit (not shown). The signal amplitude limiting unit 21 is supplied with the amplitude limiting setting value, and when the level of the IQ signal is equal to or lower than the amplitude limiting setting value, the IQ signal is directly input to the signal amplitude limiting unit 2
However, when the level of the IQ signal exceeds the amplitude limit setting value, this level is limited to the amplitude limit setting value. As a result, the level of the IQ signal output from the signal amplitude limiting unit 21 is limited to the amplitude limit setting value or less.

In this way, the peak included in the modulated wave is limited with a simple structure, and the load on the quadrature modulator and the transmission amplifier connected in the subsequent stage can be reduced.

[0009]

However, in the transmitting section of such a repeater, as shown in FIG.
The F22 is provided to limit the band of the IQ signal of the base band. Due to the overshoot of the filter characteristic of the digital LPF 22, the following problems occur.

Now, assuming that the amplitude limit setting value set by the signal amplitude limiter 21 is level B in FIG. 6A, the output IQ signal of the signal amplitude limiter 21 is a signal of level B or lower, which is It is supplied to the digital LPF 22. At this time, if overshoot does not occur in the digital LPF 22, the IQ signal of the maximum level B is digital L
Although it is not a problem because it is output from the PF 22, if an overshoot occurs in the digital LPF 22, an IQ signal having an abnormal level exceeding the level B is output from the digital LPF. The maximum level of the output IQ signal of the digital LPF 22 due to this overshoot is A.
The IQ signal having such an abnormal level is transmitted to the D / A converter 2
It is supplied to the quadrature modulator 3 and the quadrature modulator and the transmission amplifier in the subsequent stage, and the peak level is not completely suppressed.

In order to prevent this, as shown in FIG. 6B, the maximum value of the overshoot of the digital LPF 22 is expected, and the amplitude limit set value of the signal amplitude limiter 21 is set as shown in FIG. 6A. It is conceivable to set it to a level B ′ lower than the level B of It should be noted that the level C is the digital L due to the maximum overshoot in the digital LPF 22 when the amplitude limit setting value is set to the level B ′.
The level (maximum level) of the output IQ signal of the PF 22, and the level D is the average level of the output IQ signal of the digital LPF 22 including the effect of the average overshoot when the amplitude limit setting value is set to the level B ′. Is.

In this case, the output IQ of the digital LPF 22
In order to keep the signal level within the level B in FIG. 6A, the level C is made equal to the level B. In this case, the IQ signal input to the signal amplitude limiter 21 is The originally required signal components from level B ′ to level C (= level B) are lost due to the amplitude limit setting value (= level B ′) in the signal amplitude limiter 21, and the signal quality is reduced. Is deteriorated.

It is an object of the present invention to provide a transmission peak limiting circuit which solves such a problem and is capable of limiting the peak level by suppressing the deterioration of signal quality.

[0014]

In order to achieve the above object, the present invention provides a signal amplitude limiting section for limiting the amplitude of a baseband signal consisting of a code sequence for each code, and an output signal of the signal amplitude limiting section. Performs the same arithmetic processing as the digital low-pass filter for each code of the baseband signal and the digital low-pass filter with taps that limits the band, and estimates the magnitude of the filter overshoot in the digital filter, and according to the estimation result. And a filter overshoot estimation section for controlling the amplitude limitation in the signal amplitude limitation section.

Further, according to the present invention, the filter overshoot estimation unit multiplies a tap coefficient of the digital low-pass filter for each code of the baseband signal by a number equal to the number of taps of the digital low-pass filter, and the multiplication. And an adder for adding the output of the adder, and when the output of the adder is an estimation result and the estimation result is larger than a predetermined amplitude limit setting value, an amplitude limit value smaller than 1 is set. When the estimation result is equal to or less than the amplitude limit set value, the amplitude limit value having a value equal to 1 is generated and supplied to the signal amplitude limit unit. The input sign is multiplied by the amplitude limit value supplied from the chute estimation unit.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a first embodiment of a transmission peak limiting circuit according to the present invention, in which 1 is a delay unit, 2 is a signal amplitude limiting unit, 3 is a digital LPF with a tap, and 4 is a D / A converter. Reference numeral 5 is a filter overshoot estimation unit, and 6 and 7 are input terminals.

In the figure, the baseband IQ signal consisting of a sequence of sequential codes input from the input terminal 1 is
After being delayed by the delay unit 1, the signal is supplied to the signal amplitude limiting unit 2. In the signal amplitude limiter 2, the amplitude limit value α (≦ 1) supplied from the filter overshoot estimation unit 5 is supplied, and the supplied IQ signal is multiplied by the amplitude limit value α to limit the amplitude. The amplitude limited IQ signal output from the signal amplitude limiting unit 2 is a digital LPF with a tap.
After being band-limited by 3, the analog signal is converted by the D / A converter 4 and supplied to an orthogonal conversion circuit or a transmission amplifier (not shown).

The filter overshoot estimation unit 5 is supplied with the IQ signal input from the input terminal 1, observes the code sequence of the IQ signal, estimates the overshoot in the digital LPF 3 for each code, and estimates the amount and amplitude of the overshoot. An amplitude limit value α that prevents the amplitude from exceeding the limit set value when the code passes through the digital LPF 3 is generated and supplied to the signal amplitude limiter 2. The signal amplitude limiter 2 multiplies the supplied signal limit value α by the corresponding code, that is, the target code when the amplitude limit value α is created. The IQ signal input from the input terminal 1 is delayed by the delay unit 1 and supplied to the signal amplitude limiting unit 2 in order to match the timing with the code corresponding to this and enable these multiplications. ing.

Next, the method of estimating the filter overshoot from the code sequence of the baseband IQ signal in the filter overshoot estimation unit 5 and the amplitude limit value α will be described.

Now, as shown in FIG. 2, the digital LPF 3 has five cells R1, R2, R each having a tap.
3, R4 and R5 registers and cells R1 and R
2, tap coefficient C1, provided for each of R3, R4 and R5
It is assumed to be composed of multipliers of C2, C3, C4 and C5 and an adder for adding the outputs of these multipliers.

The filter overshoot estimation unit 5 also has the same structure as the digital LPF 3 for the number of cells in the register, and the overshoot for each code of the IQ signal input using such a structure. Is estimated.

Now, the code strings of the input baseband IQ signals are a, b, c, d, e, f, g, h, i, j,
.., the code of each cell of the register at time t1 is, as shown in FIG. 3, code a in cell R1, code b in cell R2, code c in cell R3, code d in cell R4, and code R5 in cell R4. Assuming that the code is e, the times t2, t3 and the time when the code period elapses.
For each t4, t5, t6, ..., As shown in FIG.
Each code moves from the cell R5 side to the cell R1 side.
In FIG. 3, each cell R1, R2, R3, R4, R5 is
The tap coefficient of C1 and C is the same as that of the digital LPF3.
2, C3, C4 and C5.

In the filter overshoot estimation unit 5, every time t1, t2, t3, t4, t5, t6 in FIG.
The calculated value F _{out_ti} (where i = 1, 2,
3, ..., 6)

[0024]

[Equation 1] These are the same as the output value of the digital LPF 3 (that is, the output value of the adder in FIG. 2), and this is the filter overshoot estimation value.

Now, focusing on the code e, the filter overshoot estimation value shown in the above mathematical expression 1 is divided into a term including the code e and a term not including the code e, and is expressed as follows.

[0026]

[Equation 2] Therefore, as a general formula,

[Equation 3] Is represented. The estimated filter overshoot value is compared with the amplitude limit setting value in FIG. 1, and the amplitude limit value α to be supplied to the signal amplitude limiter 2 is set according to the comparison result.

Then, focusing on the code e, the following equation 3
The filter overshoot estimation value F _{out —} tx for each value of x shown in (2) (that is, all of _Expression 2) is compared with the amplitude limit setting value. Then, for all the filter overshoot estimation values F _{out —} tx, when the amplitude limit setting value ≧ F _{out —} tx, even if the overshoot occurs in the digital _{LPF 3} , the level is within the amplitude limit setting value, and the amplitude limit value is set. Let α = 1.0. The amplitude limit value α is for the code e, and when the amplitude limit value α is supplied to the signal amplitude limiter 2, the delay unit 1 supplies the code e to the signal amplitude limiter 2 at this time. The code e is multiplied by the amplitude limit value α of 1.0. That is, the code e is directly output from the signal amplitude limiting section 2 without being subjected to amplitude limitation and is supplied to the digital LPF 3. In this case, the output signal of the digital LPF 3 does not exceed the amplitude limit setting value even if overshoot occurs.

With respect to the code e, if the amplitude limit set value <F _{out_tx} at any one or more of the filter overshoot estimation values F _{out_tx} , the code e exceeds the amplitude limit set value at the digital _{LPF 3.} Since there is a possibility of overshoot, it is necessary to limit the amplitude. Therefore, the amplitude limit value α <1.0. As a method of setting such an amplitude limit value α,
Now, assuming that the value of _Equation 3 when the code e is multiplied by the amplitude limit value α is F _{out_tx} ′, the amplitude limit value α is as _follows : amplitude limit set value ≧ F _{out_tx} ′ = Ax + (C (6-x) ×
e × α) That is, the amplitude limit set value −Ax ≧ C (6-x) × e × α is a value that satisfies all of x = 1 to 5.

The amplitude limit value α thus obtained is supplied to the signal amplitude limiter 2 and is multiplied by the code e supplied from the delay unit 1 at this time as described above. As a result, the code e multiplied by the amplitude limit value α becomes the digital LP.
It is supplied to F3.

In this way, the amplitude limit value α is set for the code e, but when the code f is input from the input terminal 1 from the time t2 as shown in FIG. When the filter overshoot estimated value is obtained using the means to form the amplitude limit value α and the code g is input from the input terminal 1 from the time t3, the filter overshoot estimated value is used using the same means as the code e. Is calculated to form the amplitude limit value α, and the amplitude limit value α is set for each input code.
Is calculated and is multiplied by the corresponding code in the signal amplitude limiting unit 2.

As described above, in this embodiment, in the filter overshoot estimation unit 5, the digital LPF 3
The overshoot in the digital LPF 3 is estimated by performing the same calculation as the filter calculation performed in step 2. Even if the output level of the digital LPF 3 causes the overshoot, the amplitude limit set value is set based on the estimation result. Since the optimum amplitude limit value α that does not exceed is obtained and the sign is multiplied to limit the signal amplitude, the overshoot also causes the amplitude range depending on the amplitude limit set value as shown in FIG. 6C. Therefore, it is possible to obtain a signal in the required amplitude range without quality deterioration.

By the way, in the above-described first embodiment, five calculations are required for each code, and the calculation amount is the number of taps times the calculation amount of the digital LPF 3. Therefore, it is desired to reduce the amount of calculation, but as a method therefor, the filter overshoot estimation is performed only when the peak condition for estimating the filter overshoot with a smaller number of taps than the digital LPF 3 is satisfied. There is a method of using these together.

The method of (3) adopts the configuration shown in FIG. 1 as it is. For example, in Equation 3, x = 2.
The estimation is performed using the calculations of 3 and 4 and not the calculations of x = 1 and 5. The calculation amount at this time is the digital L
Calculation amount of PF3 x (number of taps of digital LPF3-2)
Become a city. When this method is used, an error occurs in the estimated filter overshoot. Therefore, the digital L
The level of the baseband IQ signal output from PF3 may not fall within the predetermined limit amplitude range of the amplitude limit set value, but if the allowable error range is set,
The amount of calculation can be reduced by the balance between the error amount and the tap coefficient of the digital LPF 3.

FIG. 4 is a block diagram showing a second embodiment of the transmission peak limiting circuit according to the present invention, which adopts the above method, in which 7 is a multiplier, 8 is a threshold judging section, Portions corresponding to those in FIG. 1 are designated by the same reference numerals, and duplicate description will be omitted.

In the same figure, in the second embodiment, the filter overshoot estimation similar to that in the first embodiment is performed for the code at that time only when there is an operation trigger signal from the threshold value judging section 8. It is something to do. The output condition of this operation trigger signal is (a) when the value of the sign of the baseband IQ signal input from the input terminal 6 exceeds the required limit amplitude (FIG. 6) determined by the amplitude limit setting value (b). This is a case where the sign value of the IQ signal of the baseband input from the input terminal 6 is a value that is likely to exceed the required limit amplitude in the LPF 3.

In the case of the above (a), the threshold value judging section 8 compares the value of the input code with the amplitude limit setting value, and outputs an operation trigger signal when the amplitude limit setting value is exceeded.

In the case of the above (b), as shown in FIG. 4, the threshold setting coefficient β (<
1) is multiplied, and the result of this multiplication is used as a threshold to determine the threshold value.
The value of the input code is compared with, and when this threshold value is exceeded, the operation trigger signal may be output. This threshold setting coefficient β is
The maximum overshoot level of the digital LPF 3 and the peak appearance frequency (related to the calculation amount of the filter overshoot estimation unit 5) are taken into consideration. The threshold determination unit 8 does not generate an operation trigger signal for an input code having a value that does not exceed this threshold. Therefore, at this time, the filter overshoot estimation unit 5 performs the filter overshoot estimation for this code. Instead, the amplitude limit value α of 1.0 is supplied to the signal amplitude limiter 2 together with the input of this code to the signal amplitude limiter 2.

In this way, the filter overshoot estimation unit 5 does not perform the calculation of the filter overshoot estimation for the code that does not exceed the above threshold, so that the amount of calculation can be reduced. The amount of calculation can be further reduced by using the above method together with this.

Although the embodiment of the present invention has been described above, the present invention is not limited to this embodiment. For example, the number of taps of the digital LPF 3 may be other than 5.

[0040]

As described above, according to the present invention,
Even with a signal that has passed through the digital LPF, a high-quality signal can be obtained without a peak exceeding the required limit amplitude, and the influence on the quadrature modulator and the transmission amplifier can be eliminated.

Further, according to the wireless communication device of the present invention, since the above-mentioned transmission peak limiting circuit of the present invention is used as an amplifier, a single signal processing system is used for processing bidirectional signals. Therefore, the number of components can be significantly reduced, the circuit scale can be reduced, and the cost can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of a transmission peak limiting circuit according to the present invention.

FIG. 2 is a configuration diagram showing a specific example of a digital LPF in FIG.

FIG. 3 is an operation explanatory diagram of a filter overshoot estimation unit in FIG.

FIG. 4 is a block diagram showing a second embodiment of a transmission peak limiting circuit according to the present invention.

FIG. 5 is a block diagram showing an example of a conventional transmission peak limiting circuit.

FIG. 6 is a diagram showing effects of a conventional example and an embodiment of the present invention in comparison.

[Explanation of symbols]

1 delay part 2 Signal amplitude limiter 3 Digital LPF 4 D / A converter 5 Filter overshoot estimation unit 6 input terminals 7 multiplier 8 Threshold judgment section

Claims (2)

[Claims] 1. A signal amplitude limiting section for limiting the amplitude of a baseband signal consisting of a code sequence for each code, a tapped digital low-pass filter for band limiting the output signal of the signal amplitude limiting section, and the baseband signal. The same arithmetic processing as that of the digital low-pass filter is performed for each code of, the magnitude of the filter overshoot in the digital filter is estimated, and the amplitude limit in the signal amplitude limiter is controlled according to the estimation result. A transmission peak limiting circuit comprising: a filter overshoot estimation unit. 2. The multiplier according to claim 1, wherein the filter overshoot estimation unit multiplies a tap coefficient of the digital low-pass filter for each code of the baseband signal of a number equal to the number of taps of the digital low-pass filter. A value less than 1 when the output of the adder is used as the estimation result and the estimation result is larger than a predetermined amplitude limit setting value. An amplitude limit value is generated and supplied to the signal amplitude limiter, and when the estimation result is equal to or less than the amplitude limit set value, an amplitude limiter value equal to 1 is generated and supplied to the signal amplitude limiter, The transmission peak limiting circuit, wherein the signal amplitude limiting section multiplies the input code by the amplitude limiting value supplied from the filter overshoot estimating section.