JPH02206397A - Pulse width modulation system and actuator driving method through pulse width modulation system - Google Patents

Abstract

PURPOSE:To prevent occurrence of a blind zone or discontinuous characteristic and to produce an accurate pulse width modulation signal by producing a pulse width modulation signal for positive input signal from a first gate signal and producing a pulse width modulation signal for negative input signal from a second gate signal. CONSTITUTION:When an input signal S1 is positive, transistors(Tr) Q2 and Q3 in a switching circuit 8 are turned OFF while transistor Tr Q4 is turned ON. Consequently, Tr Q1 is turned ON when a first gate signal S13 is L, and current having such level as proportional to the positive level of the signal S1 flows through an actuator 18 in the direction from terminal 18a to terminal 18b. When the signal S1 is negative, Tr Q1, Tr Q4 in the switching circuit 8 are turned OFF while Tr Q3 is turned ON. Consequently, Tr Q2 is turned ON when the second gate signal S14 is L and current Ia flows through the actuator 18 in the direction from the terminal 18b to the terminal 18a.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a pulse width modulation method for converting an analog signal into a pulse width modulation signal, and a method for driving an actuator used in an optical recording/reproducing device, among others. In particular, the present invention relates to a driving method using a pulse width modulation method in which an output transistor is turned ON and OFF at a high frequency, and the ON period is pulse width modulated to control the displacement of an actuator.

As is already well known, in conventional optical recording and reproducing apparatuses, tracking control and focus control of a finely narrowed light spot are performed, and an actuator is required to move the optical components to move the light spot.

On the other hand, in recent years, there has been a demand for smaller size and lower power consumption in these devices, and a drive method based on a pulse width modulation method with high power efficiency has come to be used.

FIG. 8 shows a block diagram of a conventional pulse width modulation method for driving an actuator, and FIG. 9 shows a waveform diagram of the eighth response section. In FIG. 8, input signal S1 is applied to comparator 1 and absolute value circuit 2. In FIG. Comparator 1
is for determining the polarity of the input signal S1, and as shown in FIG. 9, the signal S1 is positive (+) with respect to the reference "O" level.
), it generates a digital output signal S2 which is "H" and when it is negative (-), it is "L". This signal S2 is applied to the inverter 3, and the signal S2 is inverted with respect to the signal S2 as shown in FIG.
I got 3.

The absolute value circuit 2 is a circuit that obtains the absolute value of the input signal S1, and as shown in FIG. 9, when the signal S1 is positive, it is equal to the signal S1, and when it is negative, the signal S1 is set to 0°.

An absolute value signal S4 inverted with respect to the level is obtained.

This signal S4 is applied to the in-phase input of the comparator 4, and a high-frequency (several tens to hundreds of kHz) triangular wave signal S5 rising from the '0' level as shown in FIG. is added, and the levels of both are compared, and when the level of the signal S4 is higher than the level of the signal S5, it becomes "°H", and when the opposite, it becomes 'Ln.
A signal S6 as shown in is obtained. This signal S6 becomes a pulse width modulated signal whose H" period increases in proportion to the level of the signal S4, that is, the absolute value of the signal S1. This signal S6 is applied to the NAND gate 6 and the NAND gate 7, and the NAND gate 6 The other input of the signal S2
and the other input of the NAND gate 7 receives the signal S
3 is added. Therefore, as shown in FIG. 9, when the signal S2 is "H", the signal S6 is output from the NAND gate 6.
A signal S7 is obtained which is in an inverse relationship with , and becomes "H" when the signal S2 is "L".On the other hand, as shown in FIG. 9, when the signal S2 is "H", the signal S7 is "H" ■1”
And when the signal S2 is "L", a signal S8 is obtained which has an inverse relationship with the signal S6.

Further, the signal 32. S3. S7.38 is switch circuit 8
added to. In the switch circuit 8, PNP l-
The emitters of transistors Ql and Q2 are both powered by ■. The emitters of NPN l-transistors Q3 and Q4 are both connected to ground. The collector of Ql and the collector of Q3 are connected to the terminals 18a of the actuator 18, .
The collectors of Q2 and Q4 are connected to 18b, and the anode side of the flywheel diode Di is grounded and the cathode side is connected to the terminal 18a, and the anode side of the flywheel diode D2 is grounded and the cathode side is connected to the terminal 18b. Connected. The base of Ql is connected to the signal 37. through a resistor R1. There is a resistor R at the base of Q2.
2 via said signal 38. The signal S3 is applied to the base of Q3 via a resistor R3, and the signal S2 is applied to the base of Q4 via a resistor R4. In order to simplify the explanation, it is assumed that these transistors operate ideally with an ON resistance of OΩ and an OFF resistance of ■.

Now, when the input signal 51 is positive, the signal S3 is
is L'', signal S8 is H'', and both Q2 and Q3 are OFF.
state, the signal S2 becomes H"", Q4 becomes ON state, and the terminal L8b becomes equal to the ground potential, so the 10th
This can be approximated by an equivalent circuit as shown in Figure (a). In the circuit shown in FIG. 10(a), Q
A current 1a proportional to the ON period of signal S7, that is, the L period of signal S7, flows from 18a to 18b.

Conversely, when signal S1 is negative, signal S2 is low and signal S7 is high.
', both Ql and Q4 are in the OFF state, and the signal S3 is "H".
”, and Q3 is in the ON state and the terminal 18a is equal to the ground potential, so it can be approximated by an equivalent circuit as shown in FIG. 10(b), and the actuator current 1a is
flows from 18b to 18a in proportion to the ON period of Q2, that is, the L period of signal S8.

Therefore, if the polarity flowing from 18a to 18b is a positive current, a current Ia proportional to the signal S1 flows to the actuator 18 as shown in FIG.

Problems to be Solved by the Invention Now, in the conventional example described above, the triangular wave generating circuit 5
An example has been described in which the output signal S5 rises from the "0" level. Next, let us consider the case where the triangular wave signal S5 rises with an offset from the "0" level.

In FIG. 12, the signal S5 has an offset voltage ■ in the positive direction. F
FIG. 8 is a waveform diagram of each part in FIG. 1st
In FIG. 2, the signal S5 is a positive voltage V. The absolute value of the signal 84, that is, the signal S1, which rises from Fl, is this ■.

, 1, the signal S6 is always "L", and the two pulse width modulated signals S7. Both S8 become H, creating a dead zone in which the "L" state does not occur, and transistors Ql and Q2 both become O.
The current Ta does not flow through the actuator 8 due to the FF state. Therefore, the relationship of the current [a to the signal S1 is also the first
As shown in Figure 3, there is a dead zone oz.

Conversely, in FIG. 14, the signal S5 has an offset voltage V in the negative direction. FIG. 8 is a waveform diagram of each part in FIG. 8 when F2 is provided. In the same figure, even if the signal S4 becomes O level, the signal S4 becomes larger than the signal S5, and at this time, the signal S4 becomes larger than the signal S5.
6 is V. , becomes "H" for a period ΔT corresponding to 2. Therefore, at the time of polarity transition when the signal Sl changes from positive to negative or from negative to positive, the pulse width (L period) of the pulse width modulation signal S7 or S8 does not pass through 0 and becomes +ΔT.
→−ΔT or −ΔT → tenΔT (the pulse width of the signal S7 is +, and the pulse width of the signal S8 is –). At the same time, the "L" period of the signal S7 or S8 with respect to the signal S1 becomes longer than that of FIG.

Therefore, as shown in FIG. 15, the relationship between the actuator current Ia and the signal S1 also has a discontinuous characteristic in which the signal 31 jumps from +Δ11 to -Δ■1 in the vicinity of "0°".

In addition, in FIG. 8, the triangular wave signal S5 and the absolute value signal S
When the speed of the comparator 4 that compares the levels of 4 is not negligibly faster than the period of the triangular wave signal, for example, the rise time 1r and the fall time 1. The relationship is 1
．． >1. When this happens, the L period of the signal S6 becomes shorter, resulting in a state as shown in FIG. do. On the contrary, 1.
>1. , the “L°” period of the signal S6 becomes longer, and the first
4 The state shown in FIG. 36 is reached, and the pulse width modulated signal 37. A discontinuous characteristic occurs in the relationship between S8 and Sl and Ia.

As described above, in the conventional example, dead zones and discontinuous characteristics tend to occur due to the offset of the triangular wave signal and the speed of the comparator, making it impossible to obtain an accurate pulse width modulation signal.

Alternatively, when applied to an actuator drive circuit and incorporated into the feedback loop of a control system, if there is a dead zone,
Even if the input signal increases or decreases in the dead zone, the current 1a flowing through the actuator does not change and the gain decreases, making it impossible to realize a highly accurate control system, or if there is a discontinuous characteristic, the input signal " For changes around the 0” level,
The actuator current changes greatly, the equivalent gain increases, and the control system becomes unstable.

Furthermore, it is difficult for a triangular wave signal that rises from the "0" level to accurately rise from the "0° level, and offsets as shown in Figures 12 and 13 tend to occur. Furthermore, the frequency of the triangular wave signal is usually A signal with a frequency of ten to several hundred kHz is used, and it is difficult to realize a comparator that is negligible with respect to the frequency of the signal.

For this reason, the dead zone and discontinuous characteristics described above also become large, making it even more difficult to realize a highly accurate control system or a stable control system.

The present invention solves the above problems and solves the problem that dead zones and discontinuous characteristics occur in the pulse width modulation signal due to the offset of the triangular wave signal, the offset of the comparator, or the difference between the rise time and fall time of the comparator. A pulse width modulation method that can prevent this and obtain a positive pulse width modulation signal, and when applied to actuator drive circuits and incorporated into the feedback loop of a control system, high precision and stable control can be achieved. A method for driving an actuator using pulse width modulation is provided.

Means for Solving the Problems In order to solve the above problems, the pulse width modulation method of the present invention uses an input inverted signal obtained by inverting an input signal, a triangular wave signal,
a first comparison signal that compares the input signal and the triangular wave signal; a second comparison signal that compares the input inverted signal and the triangular wave signal;
A first gate signal that detects a period in which the input signal is larger than the triangular wave signal and the input inverted signal is smaller than the triangular wave signal from the first and second comparison signals; obtain a second gate signal that detects a period in which the input inverted signal is smaller and larger than the triangular wave signal; the first gate signal obtains a pulse width modulation signal when the input signal is positive; It is configured to obtain a pulse width modulation signal when the input signal is negative.

Further, in the actuator driving method using the pulse width modulation method of the present invention, the ON state of the first transistor is controlled by the first gate signal, and the ON state of the second transistor is controlled by the second gate signal. It consists of

Effects of the present invention With the above configuration, the dead zone and discontinuous characteristics of the pulse width modulation signal are reduced, an accurate pulse width modulation signal is obtained, and a highly accurate and stable pulse width modulation type actuator driving method is obtained. Can be done.

Embodiment Hereinafter, a pulse width modulation method and an actuator driving method using the pulse width modulation method according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a pulse width modulation method and an actuator driving method using the pulse width modulation method in an embodiment of the present invention, and FIG. 2 is a waveform diagram of the first response section. In addition, in the following drawings, the same parts as in the conventional example are indicated using the same names and symbols.

In FIG. 1, an input signal SI is applied to the in-phase inputs of an inverting circuit 9, a comparator 1, and a comparator 11. The comparator 1 and the inverter 3 serve as signals 32 and 33 for determining the polarity of the signal S1, similar to the conventional example shown in FIG.
I am getting .

The inverting circuit 9 inverts the input signal S1 with respect to the reference voltage "0°" level and generates an input inverted signal S as shown in FIG.
9, and this signal S9 is applied to the in-phase input of the comparator 12.

On the other hand, the triangular wave generating circuit 13 generates a signal SIO as shown in FIG. 2, which is approximately symmetrical to the "0" level.
IO is applied to the opposite phase inputs of comparators 11 and 12. The comparator 11 compares the levels of the signal S1 and the triangular wave signal 310, and produces a signal s as shown in FIG.
1 is higher than the signal SIO, the signal Sll becomes "H", and vice versa, the signal Sll becomes "L". Comparator 12
In this step, the levels of the signal S9 and the signal slo are compared,
As shown in FIG. 2, a signal 12 is obtained which becomes "H" when the signal s9 is higher than the signal SIO, and becomes "L" when the signal s9 is higher than the signal SIO.

Signals sll and 312 are applied to N0R15 with an inverting input and NAND14 with an inverting input.

In NANDl 4, when the signal 312 is active and the signal 311 is "H", a signal S13 as shown in FIG. ing. In N0R15, signal 312
is "H" and the signal Sll is "L", that is, the signal S14 is "L" in the period corresponding to the difference between the H periods of the signals S11 and S12, as shown in FIG. 2. .

The signal S13 becomes a pulse width modulated signal only in the positive region of the signal S1, and as the level of the signal S1 increases, the pulse width 'L' period becomes longer, and in the negative region, the signal S13 becomes a pulse width modulated signal.
It is fixed at "H" level.

The signal S14 becomes a pulse width modulated signal only in the negative region of the signal S1, and as the level of the signal S1 increases in the negative direction, the pulse width "L" period becomes longer, and in the positive region, It is fixed at "H" level.

These signals 313, 314 and the signal 32°S3 are applied to the switch circuit 8. This switch circuit 8 is the same as that shown in the conventional column of FIG. 8, and the actuator 8 is connected thereto as in the conventional example.

Signal S2 is applied to the base of transistor Q4 via resistor R4, signal S3 is applied to the base of transistor Q3 via resistor R3, and signal S13 . S14 also
Transistors Ql and Q via resistors R1 and R2, respectively.
It is supplied to the base of 2.

Now, when the signal S1 is positive, the switch circuit 8 switches Q2. Q3
Both are in the OFF state and Q4 is in the ON state, so it is equivalent to replacing the signal S7 in FIG. 1a is 18a → 1
8b, and during the "off" period of the signal S13,
It is proportional to the positive level of signal S1. Conversely, when the signal S1 is negative, the switch circuit 8 turns off both Ql and Q4 and turns on Q3, causing the signal S in FIG. 10(b) to turn off.
8 is replaced with the signal S14, and the signal 314
When is L, Q2 becomes ON state, and the actuator 18
The current Ia flows in the direction from 18b to 18a, and is proportional to the "L" period of the signal S14, that is, the negative level of the signal S1. As a result, an actuator current Ta proportional to the signal S1 flows, similar to that shown in FIG. 11 above.

Now, in the present invention, the triangular wave signal 310 can be obtained from a circuit as shown in FIG. 3, for example. or,
FIG. 4 is a waveform diagram of the third response section.

In FIG. 3, the oscillator 16 outputs a rectangular wave signal S15 whose "'H°" period is equal to the L period, which is passed through a capacitor CI to cut off the DC voltage in the signal S15, and then sent to an operational amplifier. 23 and resistors R5, R6 (R6) R5)
In addition to the well-known Miller integration circuit composed of capacitor C2 and capacitor C2, the signal 315 rises during the "L" period,
A triangular wave signal SIO that falls during a period is obtained.

Now, using FIGS. 5 and 6, let us consider the case where an offset occurs in the triangular wave signal in the present invention. In addition, in FIGS. 5 and 6, the time axis of each signal waveform is enlarged from that shown in FIG. 2. Figure 5 shows a state in which the signal S1 is a positive voltage, and of the triangular wave signals shown in SIO in the same figure, the waveform marked by the solid line I is the waveform of the signal SIO when there is no offset voltage, and the waveform marked by the dashed dotted line ■. The waveform is positive. The waveform of the signal SIO when it has an offset voltage of Fl, the waveform indicated by the broken line (■) is V in the negative direction. F
The waveform of signal 310 is shown when it has an offset voltage of 2. Further, the signal S9 has a level that is inverted from the O level of the signal S1. The same description will be given below in FIG. 6 as well.

In Figure 5, (1), (n), (III) are
Waveforms S, 11. of each part corresponding to the states I to (3) of the signal SIO, respectively. S12. S13. S14 is written, and when an offset occurs in the signal SIO, the signal Sl
The pulse widths of the signal 312 and the pulse width of the signal 312 change or have the same amount of change, and the width of the "L" period of the signal 313, which is the difference between the pulse widths, does not change, as shown by the arrow in the figure (the time axis is Similarly, when the signal S1 is negative, the width of the "L" period of the signal S14 does not change and only the time axis moves.Also, regardless of the offset amount of the signal SIO, the signal SL When positive, the signal S14 always becomes H, and conversely, when negative, the signal 313 becomes "°H".

FIG. 6 is a waveform diagram when the signal S1 is at O level. At this time, both signals Sl and S2 are at 0 level, so the pulse width of both signals Sll 312 changes due to the offset of the signal 310, but since the widths are always the same, the signal 5
Both 13 and 314 are always H, and no current flows to the actuator.

Therefore, according to the present invention, the pulse width modulated signal and the current Ia flowing through the actuator do not change due to the offset of the triangular wave signal S10, and have a proportional relationship with the input signal without a dead zone or discontinuous characteristic.

Next, the response time of the comparators 11, 1.2 shown in FIG. 1, that is, the rise time 1 occurring in the signal S11.312
r and fall time1. Let us consider a case where the period of the triangular wave signal S10 cannot be ignored.

FIG. 7 shows a state in which the signal S1 is positive (I).

(■) and (1) are respectively (1); the state of tr=t, =o (II); the state of t, >t, >o (In); the state of t, >t, >o Signal S11. Signal S12. Signal S13° Signal S
14 is shown.

In FIG. 1, the comparators 11, 11; can be constructed from the same circuit, and their response times are also approximately equal. In particular, when these circuits are formed on the same chip of an integrated circuit,
All characteristics including response time become extremely similar. If the response times (1r, 1.) of comparators 11 and 12 are equal, the state of (n) or (I[[) in FIG. 7 is (1).
For the state of signal S11. The pulse widths of both S12 change by the same amount, and the difference between them, the width of the L period of the signal S13, does not change, but only the time axis moves as in FIG. 5 above. Therefore, according to the present invention, if the response times of the two comparators are made equal, the pulse width modulated signal and the current flowing to the actuator will not be affected by the response time of the comparator and will be proportional to the input signal. .

Effects of the Invention By having the above-described configuration, the present invention prevents the occurrence of dead zones or discontinuous characteristics in the pulse width of the input signal and the pulse width modulation signal, or in the relationship between the input signal and the current 1a. For example, when the present invention is applied to an actuator drive circuit of an optical recording/reproducing device, the accuracy of the control 11 deteriorates due to the dead zone, or the control system becomes unstable due to discontinuous characteristics. etc. can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a pulse width modulation method and an actuator driving method using the pulse width modulation method in an embodiment of the present invention, Fig. 2 is a waveform diagram of each part of Fig. 1, and Fig. 3 is a triangular waveform shown in Fig. 1. A circuit diagram of the generation circuit, Fig. 4 is a waveform diagram of each part in Fig. 3, and Fig. 5 is a waveform diagram of each part in Fig. 1 when an offset occurs in the triangular wave when the signal S1 in Fig. 1 is a positive voltage. Fig. 6 is a waveform diagram of each part in Fig. 1 when an offset voltage is generated in the triangular wave signal when the signal S1 is 0 level, and Fig. 7 shows the response speed of comparators 11 and 12 shown in Fig. 1 and each part in Fig. 1. Figure 8 is a configuration diagram showing the driving method using the pulse width modulation method in the conventional example, Figure 9 is a waveform diagram of each part in Figure 8, and Figure 1O is shown in Figure 8. The equivalent circuit diagram of the switch circuit, Fig. 11, shows the signal S in Fig. 9.
1 and actuator current 1a, Figure 12 is 8
8 is a waveform diagram of each part when a positive offset voltage occurs in the triangular wave signal S5 in the figure, FIG. 13 is a relationship diagram between the signal S1 and actuator current 1a in FIG. 12, and FIG. Triangle '$1. Figure 8 is a waveform diagram of each part when a negative offset voltage occurs in the signal S5, and Figure 15 is the waveform diagram of each part.
4 is a relationship diagram between the signal S1 and the actuator current 1a in FIG. 4. FIG. l... Comparator, 2... Absolute value circuit, 3... Inverter, 8... Actuator, 9... Inverted IL 11... ...
・Comparator, 12... Comparator, 13
...Triangular wave generation circuit, Ql, Q2...
PNP) transistor, Q3. Q4...NPN
Transistor, Sl...Input signal, S5...
... Triangular wave diagram signal, Ia ... Actuator current, SIO
... Triangular wave signal, 313 ... First gate signal, 314 ... Second gate signal. Name of agent: Patent attorney Shigetaka Awano and one other person (b) Sl, Gako Figure 14 Figure 15

Claims (2)

[Claims] (1) means for obtaining an input inverted signal by inverting the input signal;
means for generating a triangular wave signal; means for obtaining a first comparison signal by comparing the input signal and the triangular wave signal; means for obtaining a second comparison signal by comparing the input inverted signal and the triangular wave signal; means for obtaining a first gate signal for detecting a period in which the input signal is greater than the triangular wave signal and the input inverted signal is smaller than the triangular wave signal from the second comparison signal; means for obtaining a second gate signal for detecting a period in which the input inverted signal is smaller and larger than the triangular wave signal, and obtaining a pulse width modulated signal when the input signal is positive from the first gate signal; A pulse width modulation method characterized in that a pulse width modulation signal is obtained from a gate signal when an input signal is negative. (2) means for obtaining an input inverted signal obtained by inverting the input signal;
means for generating a triangular wave signal; means for obtaining a first comparison signal by comparing the input signal and the triangular wave signal; means for obtaining a second comparison signal by comparing the input inverted signal and the triangular wave signal; means for obtaining a first gate signal for detecting a period in which the input signal is larger than the triangular wave signal and the input inverted signal is smaller than the triangular wave signal from the second comparison signal; means for obtaining a second gate signal for detecting a period in which the input inverted signal is small and larger than the triangular wave signal; a first transistor whose ON state is determined by the first gate signal; is determined, and the O of the first transistor and the second transistor is determined by the first gate signal and the second gate signal.
An actuator driving method using a pulse width modulation method, characterized in that the method is configured to control an N state.