DE102006062518A1 - Input signal's phase regulating method for digital demodulator, involves replacing controlled variable by modified controlled variable in range between basic and upper threshold values on reaching and/or falling below lower threshold value - Google Patents

Abstract

The method involves regulating a phase of input signals based on a phase error-dependent controlled variable that is confined to a range between upper and lower threshold values respectively above and below a basic value. The variable is replaced by a modified controlled variable in a range between the basic value and the lower value on reaching and/or exceeding the upper value. The controlled variable is replaced by the modified controlled variable in a range between the basic value and the upper threshold value on reaching and/or falling below the lower threshold value. An independent claim is also included for a device for phase regulation, with a delimiting arrangement.

Description

The The invention relates to a method for phase control the preamble features according to claim 1 or 8 or to a device for performing of such a procedure.

For example Phase locked loops are used in digital demodulators. In the context of a phase control by means of such a phase locked loop becomes common a phase of an input signal is regulated as a function of a phase error-dependent controlled variable, where the controlled variable to a Range between an upper threshold above an underlying and a lower threshold below the underlying becomes. The controlled variable is dependent phase errors of successive data values of the input signal determined. For this purpose, in the phase-locked loop for phase control usually a Measuring device used, which z. B. as CORDIC, that is as a Coordinate rotator, realized.

The [x1] formation of the phase error Φ _e is usually formed by a difference of a desired value Φ _soll and an actual value Φ _is the phase of the input signal according to Φ e (n) = [Φ should - Φ is (n)] modulo Φ amb . where n denotes an associated sample of the time value sequences of the phase error Φ _e and other phase values Φ _otherwise and Φ _amb denotes a base phase.

In an integrator of a controller, this phase error Φ _{e is} accumulated to the controlled variable RI. An output value of the controller is fed as the controlled variable RI an adjusting device, which rotates the instantaneous phase of the input signal, that is the actual value of Φ _is. A corresponding time sequence of integrator states of such a controller as a controlled variable sequence RI (n) of the controlled variable RI results from summation of an initial state of the controlled variable RI ₀ RI (n) = RI (n-1) + k i · Φ e , with RI (0) = RI 0 . where k _{i describes} a further control factor in a manner known per se.

Usually, the value range of the integrator is limited in magnitude to a maximum value. Accordingly, the controlled variable RI is limited to a range between an upper threshold RI _max above an underlying and a lower threshold -Ri _max below the base value. In a control system in which such a limitation occurs, due to the ambiguity of the phase, coupling situations may occur which cause the accumulator to "hang" in the limitation. This leads to the fact that the control is no longer based on the base value or the setpoint value Φ _soll but gets stuck in the range of the threshold value. In such a case, in which the control remains in an undesired control state, external control of the phase-locked loop by means of a system control device, for example, must initiate a restart of the control, for example by restarting the accumulation starting from the initial state of the controlled variable RI ₀ [x2]. ,

Possible [x3] is according to a further approach to the control an extension of the control range of the controlled variable RI for a proportional controller. A proportional controller is always fed directly without integration, a phase difference. In phase locked loops, the controlled variable RI is modular. 2 exemplifies the ambiguity of the phase, wherein a value of the controlled variable RI in the complex-valued plane with the real axis Re and the imaginary axis Im circulates in a circular path. An intersection of the circular path with the real axis forms both the lower threshold value with the value "0" and the upper threshold value with the value "2π". However, the real phase difference can assume values greater than 2π. The maximum possible directly measurable phase deviation is thus limited to 2π, whereby larger phase deviations are wrapped [x4]. However, a break is only recognizable for phase difference values smaller than π. In a simple phase-locked loop the phase is therefore z. B. limited to 2π. Due to this non-linearity, linear control behavior can no longer be achieved, and the possibly applied analysis methods in the frequency domain are no longer valid. The problem arises especially with slow control circuits, where the phase error is essentially generated by a frequency error [x5].

The The object of the invention is a method and a device to propose for the phase control, which allow a more robust fishing behavior and a stay in control states, in particular a persistence in the threshold range prevented.

These Task is solved by the method for phase control with the features according to claim 1 or 8 or by the device for phase control with the features according to claim 18. Advantageous embodiments are the subject of dependent claims.

Preferably, [x6] is accordingly particularly a phase control method in which a phase of an input signal is controlled in response to a phase error dependent controlled variable, wherein the controlled variable is limited to a range between an upper threshold above the base value and a lower threshold below the base value and wherein the control variable when reaching and / or exceeding the upper threshold value is replaced by a modified control variable in the range between the base value and the lower threshold or its amount and / or the control variable is replaced when reaching and / or falling below the lower threshold value by a modified control variable in the range between the base value and the upper threshold.

The Controlled variable can be wrapped when replacing by replacing the upper or the lower threshold at least reaching the current value the controlled variable is a value used a current new control variable which is the value of the other lower threshold or upper Threshold.

The control variable can be wrapped during replacement by deducting a value from the current value of the controlled variable or by adding to the current value of the controlled variable a value which corresponds to the maximum value range of the control range. The controlled variable is especially wrapped during replacement according to if RI (n)> RI Max , then RI (n) follows: = RI (n - 2 · RI Max ) and if RI (n) ≤ -RI Max , then RI (n) follows: = RI (n + 2 · RI Max ).

The rule variable can be wrapped at replacement by performing an addition in two's complement. Preferably, RI _max - 1 corresponds to the largest positive value in the two's complement representation. In a conversion by means of a hardware circuit, this leads to the fact that the manipulated variable coming from the integral component of the controller is inverted immediately in its sign. As a result, a stable negative feedback state is forced out of a potentially unstable positive feedback situation.

The Thresholds must preferably not identical to the limits of a permissible maximum Value range can be set but can also be smaller than such Limits of the permissible maximum value range.

Prefers also becomes independent a phase control method in which a phase of an input signal dependent from a phase error dependent Controlled variable is, the controlled variable to a Range between an upper threshold above an underlying and limits a lower threshold below the Underlying and where a number of modulo breaks are counted and limited. Instead of a simple integrator, which calculates the differences of successive ones Input values dx (n) added up, so only the number the modulo breaks counted and limited, while the actual data value x (n) is not integrated and stored becomes.

One actual data value is thus advantageously not integrated and not saved. phase breaks can be captured and the controlled variable, in particular a proportional part of the controlled variable can be detected every time be limited to a phase change. The controlled variable or a proportional component of the controlled variable can be simple Way limited each time a phase change is detected and by 2π or be extended by -2π.

One such method is used in particular if it is assumed is that successive phases by less than half Control range, in particular by less than π differ from each other.

Of the upper threshold and / or lower threshold can be set to Many times half a permissible one Value range are set. The upper threshold and / or the lower threshold may in particular be a multiple of a power of two half the permissible Value range are set.

The controlled variable can be formed by summing an initial state of the controlled variable RI ₀ to RI (n) = RI (n-1) + k i · Φ e (n), with RI (0) = RI 0 . where k _{i describes} a further control factor in a manner known per se.

The Controlled variable can optionally after a value replacing the actual instantaneous value performing Control process temporary either exceed the upper threshold set by the control process or fall below the lower threshold controlled by the control process.

The control variable can be wrapped during replacement by at least errei instead of one of the upper and the lower threshold At the instantaneous value of the control variable, a value of a current new control variable is used, which corresponds to the value of the other lower threshold value or upper threshold value.

Independently advantageous is a phase control device by the method of second approach with a break counter for detecting phase changes, a Limiting arrangement Limit the controlled variable with each entry of a Phase break and a multiplier to multiply a such limited value with the amount or a multiple of the Amount of half possible Control range [x7].

The both approaches thus aim at the two mutually different setting parameters, the permissible Maximum value or the permissible Phase difference, a phase control starting with a combination the two approaches is particularly advantageous.

Provided Thus, a method or a device or circuit arrangement, with which a phase locked loop for in particular digital demodulators is optimized by, firstly, prevents the phase locked loop in control states he remains, he no longer without external intervention on z. B. leave the system controller, and secondly enables more robust fishing behavior becomes.

One embodiment with different embodiments will be explained below with reference to the drawings. Show it:

1 a phase control diagram with a representation of a positive feedback with phase change,

2 a representation of the complex-valued level to illustrate an ambiguity of the phase,

3 a graphic illustration of a control curve of the controlled variable with phase-shift compensation and

4 an equivalent circuit diagram for an exemplary circuit arrangement for an extended control area with limitation of a break counter.

1 shows an exemplary state of a controlled variable RI over a progressive time t away. The controlled variable RI is limited to a value range between an upper threshold RI _max and a lower threshold R _max . In particular, in the middle between the two threshold values RI _max , -RI _max is a base value, in this case, for example, the value "0". At the same time, the base value forms the target value Φ _soll , to which the phase is to be regulated.

In the illustrated example of the sequence of values of the controlled variable RI, that is, the integrator content of a corresponding phase locked loop, the controlled variable RI runs in the "wrong" direction, that is, for example, the upper threshold RI _max out. In principle, upon reaching of this upper threshold value RI _max is the risk _that under unfavorable circumstances the input controlled variable, i.e. the actual value of Φ, the integrator and hence the controlled variable RI in the limitation, which is formed by the upper threshold RI _max, depend stays without ever getting to the correct target value Φ _should come.

In order to prevent the risk of getting stuck, on reaching and / or exceeding the upper threshold RI _max a phase change is performed, as shown 1 is shown clearly. By wrapping the controller comes back in a negative feedback situation and may eventually to the target value Φ _to einregeln, as is illustrated for the further course of time.

The break can be carried out in a simple manner by using the value as the instantaneous controlled variable RI _x 'in the integrator instead of the instantaneous value of the controlled variable RI _x reaching or exceeding the upper threshold RI _max corresponds to the value of the lower threshold - R _max or other value in the range between the setpoint Φ _soll and the lower threshold - R _max .

In this case, a method is particularly preferred in which a value is subtracted from the instantaneous value of the controlled variable RI _x , which value corresponds to the, in particular, maximum value range 2 * RI of the control range. This is exemplified in 1 illustrated by two crosses. The upper of the two crosses sketches the current value of the current controlled variable RI _x with a value that exceeds the upper threshold RI _max by a certain amount b. By changing the phase by the maximum value range 2 · RI of the control range, the new instantaneous controlled variable RI _x 'is correspondingly inserted by this amount b above the lower threshold value -RI _max .

In such a procedure, a coupling situation is thus counteracted in that the integrator state, when the threshold value is exceeded, is offset by its entire value range. That is, the following nonlinear op ration is carried out: if RI (n)> RI Max , then RI (n) follows: = RI (n - 2 · RI Max ) and if RI (n) ≤ -RI Max , then RI (n) follows: = RI (n + 2 · RI Max ).

Accordingly, reaching or falling below the lower threshold value -Ri _{max is also} taken into account.

In a hardware implementation of such a controller integrator, such a behavior may preferably be carried out by an addition in two's complement, where RI _max - 1 corresponds to the largest positive value in the two's complement representation. As a result, the manipulated variable coming from the integral component of the controller is inverted immediately in its sign. As a result, a stable negative feedback state is forced out of a potentially unstable positive feedback situation.

Independent of The use of fixed thresholds can also provide variable thresholds be determined. Theoretically possible is also not, the thresholds are not identical to the limits the permissible maximum value range but smaller than such limit values the permissible maximum range of values [x8].

following the control of a proportional controller is advantageous as independent implementable concept or as combinable with the above approach Concept described. The starting point is the idea that a change does not become too big may, otherwise too big Phase difference arises, which is why instead of the change in accordance with the above Concept the limitation is used. As a proportional controller has no memory or integrator, breaks are counted.

Of the Control range of the proportional controller can be extended if the Prerequisite that successive phases by less than half Control range, ie π, from each other depart than fulfilled can be viewed. In this case, phase breaks can be detected become. In the case of a positive phase change, the controlled variable would increase by + 2π and in the case of a negative phase shift extended by -2π. In the case of QPSK modulation (QPSK Quadrature phase shift keying) is the ambiguity of the phase that is the one Modulo range, only π / 2.

This behavior can be created by first "differentiating" the RI variable and then "integrating" it. Mathematically, this can be descriptively described by the condition RI (n) = RI (n-1) + (x (n) -x (n-1)) mod (2M) with z. BM = π and x (n) as a current input value of a control loop.

Assuming that RI (-1) = 0 and x (n - 1) = 0, this results in an illustrated starting sequence RI (0) = 0 + (x (0) - 0) = x (0), RI (1) = RI (0) + (x (1) - x (0)) = x (1) and RI (2) = RI (1) + (x (2) - x (1)) = x (2).

In the case of a break, that is, in the case where the unevaluated equivalent value of the control variable x '(3) would become ≥ 2π, its magnitude reduces to x (3) = x' (3) -2π. Under these conditions, this results in the third value of the sequence RI (3) = RI (2) + ((x (3) - x (2) mod 2π) = x '(3).

Due to the successive differentiation and integration, assuming that the difference of successive values is smaller than M, this results in an untransformed initial value. The typical course of a controlled variable RI (n) over time is shown 3 illustrated.

Also in such cases can, as already indicated above, to avoid limit states Break at a multiple of M, usually at a power of two from M, performed become. This is for the input quantity of the proportional component However, a controller does not always make sense.

Accordingly, an extended proportional control range with a limitation is preferred. In practical applications, a limitation to maximum and minimum control deviations makes sense in the proportional component in order to achieve a quasi-stabilization and acceleration of the controller or of the method for phase control. When limiting a breakover compensation integrator U as an exemplary embodiment to a maximum value U _max , however, the problem arises that, due to the limitation, the input value x (n) is no longer x '(n) mod (M), since x' (n) has been limited to the maximum value U _max .

If the operation of such a control process _falls below the lower limit value as a lower threshold value RI _max , the result is as follows correct from now on no synchronization of the control variable RI (n) mod (M) and the input value x (n) given more. This means that the phase controller is no longer on the original target value, z. "0", but controls to a random value within the modulo range.

This problem can be illustrated mathematically by U (n) = U Max + (x (n) -x (n-1)) mod (M) = U Max - dx (n)! = X (n) mod (M), where dx (n) describes a difference of successive input values. To avoid such inequality, a two-stage solution is proposed according to a particularly preferred embodiment.

Instead of a simple integrator, which calculates the differences of successive ones Input values dx (n) added up, only the number of modulo breaks is counted and limited, while the actual data value x (n) is not integrated and stored becomes.

Circuit technology illustrates this by the equivalent circuit diagram according to 4 , The input value x (n) becomes an adder 10 , a delay T and another adder 11 created. A delayed output value of the delay element T is a subtraction input of the first adder 10 created and thus subtracted from a temporally subsequent input value. An output value of the adder 10 forms the difference dx (n) of successive input values x (n) and becomes a break counter 12 created. The break counter 12 counts the number of modulo-breaks of the differences dx (n) of the input values x (n). An initial value of the breakover counter 12 becomes a limitation circuit 13 for limitation to a maximum and / or minimum permissible value. The output value of the limiting circuit 13 is done by means of a multiplier 14 multiplied by the upper limit 2M. The multiplication result of the multiplier 14 becomes another addition input of the further adder 11 created and the currently applied input value x (n) added up. The further adder 11 then outputs the modified current input value x '(n).

outgoing of an input sequence of input values x (n) thus becomes a Difference dx (n) of successive input values x (n) formed. If a modulo break of this difference size occurs, that is if x (n) -x (n-1) ≥ M or x (n) -x (n-1) ≦ -M, a positive or a negative break is counted. Of the signed value of the break counter is limited and then with 2M, d. H. the original one Value range of the modular input multiplied. At a Implementation in two's complement is this by a simple shift the bit position can be implemented. The shifted break counter becomes combined with the input value x (n). This gives you the numbers range extended size x '(n), which has larger input values of the proportional component, thus obtaining a faster or largely linear regulation.

Advantageous on such an implementation is also that for the accumulator just a word width for the number of breaks occurring in the limitation sufficient is required. In particular, the lower bits do not need as they are directly the input sequence of input values x (n) can be removed.

Claims (18)

Method for phase control, in which - a phase (Φ _ist ) of an input signal is regulated as a function of a phase error-dependent controlled variable (RI), - wherein the controlled variable (RI) is limited to a range between an upper threshold value (RI _max , 2M) above a Base value (0; M) and a lower threshold (-Ri _max ; 0) below the base value (0; M) is limited, characterized in that - the controlled variable (RI) upon reaching and / or exceeding the upper threshold (RI _max ) is replaced by a modified control variable (RI ') in the range between the base value (0) and the lower threshold value (-RI _max ) or its magnitude and / or - the controlled variable (RI) upon reaching and / or falling below the lower threshold value ( -RI _max ) is replaced by a modified controlled variable (RI ') in the range between the base value (0) and the upper threshold value (RI _max ). Method according to Claim 1, in which the controlled variable (RI) is wrapped during replacement by a value of a current new value instead of a current value of the controlled variable (RI _x ) at least reaching the upper or lower threshold value (RI _max , -R _max ) Controlled variable (RI _x ') is used, which corresponds to the value of the other lower threshold (-RI _max ) or upper threshold (RI _max ). Method according to Claim 1 or 2, in which the control variable (RI) is wrapped during replacement by subtracting a value from the current value of the controlled variable (RI _x ) or by adding a value to the current value of the controlled variable (RI _x ) , which corresponds to the maximum value range (2 · RI) of the control range. Method according to Claim 3, in which the controlled variable (RI (n)) is wrapped during replacement according to if RI (n) ≥ RI Max , then RI (n) follows: = RI (n - 2 · RI Max ) and if RI (n) ≤ -RI Max , then RI (n) follows: = RI (n + 2 · RI Max ). Method according to any preceding claim, in which the controlled variable (RI) is wrapped at replacement by an addition in two's complement accomplished becomes. The method of claim 5, wherein RI _max - 1 corresponds to the largest positive value in the two's complement representation. In a conversion by means of a hardware circuit, this leads to the fact that the manipulated variable coming from the integral component of the controller is inverted immediately in its sign. As a result, a stable negative feedback state is forced out of a potentially unstable positive feedback situation. Method according to any preceding claim, in which the thresholds are not identical to the limits of a maximum allowable range be set but smaller than such limits of the maximum allowable Value range are set. Method for phase control, in particular according to a preceding claim, in which - a phase (Φ _ist ) of an input signal is regulated as a function of a phase error-dependent controlled variable (RI), - wherein the controlled variable (RI) is limited to a range between an upper threshold value (RI M) is limited, characterized in that - counting a number of modulo-breaks and limited; _max; 2M) above a base value (0, M) and a lower threshold value (-RI _max, 0) below the base value (the 0th A method according to claim 8, wherein an actual Data value (x (n)) is not integrated and stored. Method according to Claim 8 or 9, in which phase changes (2π → 0) are detected and the controlled variable (RI (n)), in particular a proportional component of the controlled variable (RI (n)) by limitation the maximum number of phase breaks is limited. Method according to Claim 10, in which the controlled variable (RI (n)) or a proportional component of the controlled variable (RI (n)) at each detection a phase change is limited and extended by 2π or -2π. A method according to any one of claims 8 to 11, which uses will, if it is assumed that successive phases less than half the control range, in particular less as π from each other differ. Method according to one of Claims 8 to 12, in which the upper threshold value (RI _max ; 2M) and / or the lower threshold value (-Ri _max ; 0) are multiples of half the permissible value range (2 x Rimax> 2 x M). is set. Method according to Claim 13, in which the upper threshold (RI _max ; 2M) and / or the lower threshold (-Ri _max ; 0) are multiples of a power of 2 (2 ^N-1 ) of half the permissible value range (2 x Rimax>; 2 · M) is set. Method according to one of Claims 8 to 14, in which the controlled variable (RI (n)) is formed by summation of an initial state of the controlled variable (RI ₀ ) RI (n) = RI (n-1) + k i · Φ e , with RI (0) = RI 0 . where k _{i describes} a control factor. A method according to any preceding claim, wherein the controlled variable (RI (n)) after a value replacing the actual instantaneous value Control process temporary either the upper threshold value controlled by the control process (2M) or the lower threshold value controlled by the control process (0) falls below. Method according to one of the preceding claims, in which the controlled variable (RI (n)) is wrapped during replacement by substituting, instead of a current value of the controlled variable (RI _x ) at least reaching the upper or lower threshold value (RI _max , -R _max ) Value of a current new control variable (RI _x ') is used, which corresponds to the value of the other lower threshold (-RI _max ) or upper threshold (RI _max ). Device for phase control by means of a method according to one of claims 8 to 15 with a break counter ( 12 ) for detecting phase changes (2π → 0), a limiting arrangement ( 13 ) Limiting the controlled variable (RI (n)) each time a phase break is detected and a multiplier ( 14 ) for multiplying such a limited value by the amount of the allowable value range (2M) of the input signal (x (n)).