JPS63250918A - A/D conversion circuit - Google Patents

Abstract

PURPOSE:To enable a dynamic range to be set arbitrarily and to realize high sensitivity and low cost, by supplying an input reference voltage from both sides of a resistance ladder circuit which forms reference potential, and changing the voltage value of the input reference voltage gradually according to the level of an input analog signal. CONSTITUTION:A range control circuit RC monitors digital output signals D0-Di supplied from an encoder ENC, and forms a range control signal rc, and supplies it to a reference voltage switching circuit. And when the amplitude of the input analog signal vin exceeds the absolute values of the reference voltages VH2 and VL2, the range control signal (rc) is set a low level, and when it is less than the absolute values, the range control signal is set at a high level. Therefore, to the resistance ladder circuit, the reference voltages VH1 and VL1 assumed as comparatively large absolute values, or the reference voltages VH2 and VL2 assumed as comparatively small absolute values are supplied. Then, the dynamic range of an A/D conversion circuit is set a high or low level.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an A/D conversion circuit, and relates to a technique that is effective for use in, for example, an instantaneous comparison type A/D conversion circuit.

[Conventional technology]

Instantaneous comparison type (fully parallel comparison type) A/ There is a D conversion circuit. This instantaneous comparison type A/D conversion circuit includes a plurality of voltage comparison circuits VCI to VC, as shown in FIG.
n 7! l<provided. The input analog signal Vin is commonly input to one input terminal of these voltage comparison circuits, and the corresponding reference potential Vl-vn is input to the other input terminal. These reference potentials connect the input reference voltage V ref to the series resistors R1 to R1 of the resistor ladder circuit.
It is formed by dividing the pressure at Rn.

The output signals of voltage comparison circuits vct to VCn are output from encoder E.
A digital output signal D of 1+1 pint is supplied to the NC.
o-Di is formed.

For instantaneous comparison type A/D conversion circuits, for example, 198
Published by Nikkan Kogyo Shimbun, November 2005, Iwao Sagara, 'A/D-D/A Conversion Technology of the Microcomputer Age', pages 82-84.
It is written on the page.

[Problem that the invention seeks to solve]

The inventors of the present invention have found that when the instantaneous comparison type A/D conversion circuit described above is used in, for example, a digital servo mechanism for optical disks, the following problems occur. In other words, an analog signal input from a sensor or the like in a digital servo mechanism is, for example, a second
As shown in the figure, the amplitude becomes relatively large at startup, and becomes relatively small when the automatic control by the servo mechanism is converged. The performance of this optical disk system depends on the sensitivity of the servo mechanism after convergence, and the sensitivity of this servo mechanism is determined by the twin resolution of the A/Di conversion circuit. However, in order to increase the sensitivity of the servo mechanism, if the quantum resolution of the A/D conversion circuit is designed to correspond to a relatively small amplitude analog signal after convergence, it will be difficult to deal with the relatively large amplitude analog signal at startup. Therefore, a huge number of voltage comparison circuits are required, which hinders cost reduction of the A/Di conversion circuit.

Furthermore, if a voltage comparison circuit is provided in association with an analog signal of relatively large amplitude at the time of startup with cost in mind, the sensitivity to an analog signal of relatively small amplitude at the time of convergence will be significantly reduced.

An object of the present invention is to provide an A/D conversion circuit that can arbitrarily set a dynamic range. Another object of the invention is to provide a highly sensitive and low cost servomechanism.

The above and other objects and novel features of this invention include:
It will become clear from the description of this specification and the accompanying drawings.

Means for Solving Problem C] A brief overview of typical inventions disclosed in this application is as follows.

That is, an input reference voltage is supplied from both sides of a resistor ladder circuit that forms a reference potential, and the voltage value of this input reference voltage is changed in steps according to the level of an input analog signal.

[For production]

According to the above means, the dynamic range of the A/D conversion circuit can be set to a predetermined dynamic range according to the voltage value and voltage difference of the input reference potential according to the level of input analog No. 13, and It is possible to reduce the quantum resolution of the A/D conversion circuit and partially increase its sensitivity without adding a voltage comparison circuit.

〔Example〕

FIG. 1 shows a circuit block diagram showing an embodiment of an A/D conversion circuit to which the present invention is applied. This A/
Although the D conversion circuit is not particularly limited, it is included in a digital servo mechanism for optical disks. Each circuit element and the circuit elements constituting each block in FIG. 1, together with the circuit elements constituting other blocks of the digital servo mechanism, are manufactured using a single piece of monocrystalline silicon, etc., using known MO3 integrated circuit manufacturing technology. Formed on a semiconductor substrate. In the figure, the MOSFET whose channel (bank gate) portion is marked with an arrow is a P-channel type, and is distinguished from the N-channel MO3FET whose channel (bank gate) portion is not marked with an arrow.

Although the A/D conversion circuit of this embodiment is not particularly limited,
Input analog signal Vi formed by a reflected light sensor etc.
n, and i+1 bit digital output signal Do-D
form i. These digital output signals DO~Di
is supplied to other circuit blocks of the digital servo mechanism, and is used, for example, to set the position of the laser beam with respect to the optical disk and to control the focus. The input analog signal Vin supplied from the sensor has a relatively large one-stroke width when the servo mechanism is activated, and has a relatively small amplitude when the position setting by the servo mechanism has converged. In the A/D conversion circuit of this embodiment, since it is necessary to increase the sensitivity after the digital servo mechanism converges, the level of the input analog signal Vin is determined by monitoring the digital output signal DO-Di, and the range control signal rc is A range control circuit RC is provided. Two levels of reference voltages VHI and VLI and VH2 and VL2 are selectively supplied to the resistance ladder circuit of the A/D conversion circuit in accordance with the range control signal rc. Thereby, the dynamic range of the A/D conversion circuit is controlled in stages, and its quantum resolution is partially improved when the servomechanism converges.

In FIG. 1, an input analog signal Vin supplied from a reflection light sensor (not shown) is sent to n voltage comparator circuits V.
It is commonly supplied to one input terminal of CI to VCn. The other input terminals of these voltage comparison circuits VCt to VCn are supplied with corresponding reference potentials 1 to Vn from the resistance ladder circuit, respectively. Non-inverted output signals and inverted output signals of voltage comparison circuits VCt to VCn are supplied to encoder ENC.

The voltage comparison circuits VCI to VCn each have a basic configuration of a highly sensitive differential amplifier circuit. These voltage comparison circuits vc
i to VCn compare the level of the input analog signal Vin supplied to one input terminal with the reference potentials V1 to Vn supplied to the other input terminal, respectively. Although not particularly limited, when the level of the input analog signal Vin is lower than the corresponding reference potentials Vl to Vn, the voltage comparison circuits VC1 to
The non-inverted output signal of VCn becomes low level, and its inverted output signal becomes high level. On the other hand, when the level of the input analog signal Vin becomes higher than the corresponding reference potential Vl-Vn, the non-inverted output signals of the voltage comparison circuits VC1 to VCn become high level, and the inverted output signals become low level.

The resistance ladder circuit is composed of fi+1 voltage dividing resistors R1 to Rn+1 connected in series.

This resistance ladder circuit includes, but is not limited to, P-channel MO3FETs QI to Q4 and N-channel MO3FETs.
Two-stage reference voltages VHI/VH2 and VLI/VL are set via a reference voltage switching circuit consisting of FETs Q5 to Q8.
2 is selectively supplied. That is, the reference voltage VHI is supplied to the resistor R1, which is one end of the resistance ladder circuit, through the P-channel MO3FET Q2 and the N-channel MO3FET Q6, which are in parallel configuration, although not particularly limited, and the P-channel MO3FET Q6, which is in parallel configuration. MO3FET
A reference voltage VH2 is supplied via QL and an N-channel MO3FET Q5. Similarly, the resistor Rn+1, which is the other end of the resistor ladder circuit, has a P-channel MOS FETQ 4 and an N-channel MO3FE connected in parallel.
The reference voltage VLI is supplied via TQ8, and the reference voltage VL is supplied via the parallel P-channel MO3FETQ3 and N-channel MOSFETQ7.
2 is supplied.

Although not particularly limited, the reference voltage VHL is a relatively high positive voltage, and the reference voltage VH2 is a relatively low positive voltage. Further, the reference voltage VLI is a negative voltage whose absolute value is relatively large, and the reference voltage VL2 is a negative voltage whose absolute value is relatively small.

MO3FETQ2. Q4 and Q5. At the gate of Q7,
A range control signal rC is commonly supplied from a range control circuit RC which will be described later. Also, MO3FETQI, Q3 and Q6. The gate of Q8 is commonly supplied with an inverted signal of the range control signal rc by the impark circuit Nl, that is, an inverted range control signal rc.

When the range control signal "C" is set to low level and the inverted range control signal "C" is set to high level, MOS F E
Both T Q 2 and Q6 and Q4 and Q8 are turned off, and MO5FETQI and Q5 and Q3 and Q7 are both turned off. As a result, reference voltages VHI and VLI having relatively large absolute values are supplied to both ends of the resistance ladder circuit.

For this reason, the stepwise basis ilf! supplied to each voltage comparator circuit V Cl = V Cn! The potential interval between the potentials Vl to Vn is expanded, the dynamic range of the A/D conversion circuit is increased, and the quantum resolution thereof is made coarser. On the other hand, when the range control signal rc is set to high level and the inverted range control signal rc is set to low level, the MO3FET
QI-Q5 and Q3/Q7 are both turned on, and MO3FETQ2/Q6 and Q4/Q8 are both turned off.

As a result, reference voltages VH2 and VL2 having relatively small absolute values are supplied to both ends of the resistance ladder circuit. Therefore, the potential interval between the stepwise base potentials Vl-Vn supplied to each voltage comparator circuit VC1 to VCn is reduced, the dynamic range of the A/D conversion circuit is reduced, and its quantum resolution is improved. be done. At this time, needless to say, base 4! By appropriately selecting the voltage value and voltage difference between voltages VH2 and VL2, the dynamic range of the A/D conversion circuit can be set arbitrarily.

The encoder ENC is configured by a combinational circuit including, but not limited to, a plurality of logic gates. The encoder ENC calculates t based on the non-inverted output signal and the inverted output signal supplied from the voltage comparison circuits VC1 to VCn.
+1 bit digital output signal DO-Di is formed. That is, the level of the input analog signal Vin is instantaneously determined by the voltage comparator circuit C1-VCn, and this stepwise determined level is converted into a binary code by the combinational circuit of the encoder ENC.

The digital output signals DO to Di formed by the encoder ENC are supplied to other circuit blocks (not shown) of this digital servo mechanism, and are used as control signals for, for example, controlling the position and focus of the laser beam on the optical disc. , are supplied to the range control circuit RC of the A/D conversion circuit.

The range control circuit RC monitors the digital output signals DO to Di supplied from the encoder ENC, forms the range control signal rc, and supplies it to the reference voltage switching circuit. That is, the range control circuit RC determines whether the amplitude of the input analog signal Vin exceeds the absolute value of the reference voltages VH2 and VL2 based on the combination of the digital output signals DO to Di. Although not particularly limited, the range control circuit RC has an input analog signal Vi
When the amplitude of n exceeds the absolute value of reference voltages VH2 and VL2, range control signal re is set to low level. Also,
The range control circuit RC sets the range control signal rc to a high level when the amplitude of the input analog signal Vin is smaller than the absolute values of the reference voltages VH2 and VL2.

As mentioned above, by increasing the amplitude of the input analog signal Vin and setting the range control signal rc to a low level,
Reference voltages v1 (1 and VL, 1) having relatively large absolute values are supplied to the resistance ladder circuit, and the dynamic range of the A/D conversion circuit is increased. Also, the amplitude of the input analog signal Vin is decreased. By setting the range control signal re to a high level, reference voltages VH2 and VL2 having relatively small absolute values are supplied to the resistance ladder circuit, and the dynamic range of the A/D conversion circuit is reduced.

The range control signal rc formed by the range control circuit RC is supplied to the reference voltage switching circuit, and
Digital output signal DO as digital output signal DC
~Di is transmitted to other circuit blocks (not shown) of the digital servo mechanism.

FIG. 2 shows a signal waveform diagram of an embodiment of a digital servo mechanism including the A/D conversion circuit of this embodiment. In the same figure, the signal waveform at the beginning of startup in the digital servo mechanism for setting the position of the laser beam for the optical disk is illustratively shown as a solid line, and the level of the reference voltage supplied to the resistance ladder circuit is shown as an example. Indicated by a dashed line.

In FIG. 2, although not particularly limited, the laser beam is set at a predetermined start position upon activation, and then gradually moved to approach the groove position of the optical disc. Accordingly, the input analog signal Vin input from the reflected light sensor to the A/D conversion circuit once rises to a relatively large positive level, then decreases toward a relatively large negative level of absolute value, and the optical disc crosses the zero level at the center of the groove. In the digital servo mechanism of this embodiment, the arrival of the laser beam at a predetermined groove position is determined by detecting that the input analog signal VLn once reaches a relatively large positive level, then decreases and crosses the zero level. identify. Thereafter, the digital servo mechanism controls the position of the laser beam by driving, for example, a voice coil motor for movement so that the absolute value of the input analog signal Vin becomes small.

In the A/D conversion circuit, since the input analog signal Vin is set to a relatively small level at startup, the range control signal "C" is set to a high level.As a result, the resistor ladder circuit receives a relatively small absolute value. The reference voltage V
H2 and VL2 are supplied to increase the sensitivity of the A/D conversion circuit. When the level of the input analog signal Vin gradually increases and exceeds the reference voltage VH2, the range control signal rC is set to a low level. As a result, reference voltages VHI and VLI having relatively large absolute values are supplied to the resistance ladder circuit, and the sensitivity of the A/Di conversion circuit is reduced. Therefore, the A/D converter circuit can handle the input analog signal ■in having a relatively large absolute value.

When the laser beam approaches the groove position of the optical disc, the input analog signal Vin becomes a relatively low level, and the range control signal rc is brought back to a high level. As a result, A
The sensitivity of the /D conversion circuit is increased, and the digital servo mechanism can accurately identify the zero level crossing of the human-powered analog signal Vin.

Thereafter, since the position of the laser beam is controlled by the digital servo mechanism, the input analog signal Vin is in a vibration state with a relatively small amplitude.

Furthermore, during this time, the vibration amplitude of the input analog signal Vin is reduced, so that the A/D conversion circuit becomes highly sensitive, and the position control of the laser beam by the digital servo mechanism is performed with high precision.

As described above, the A/D converter of this embodiment has the digital output signal Do-
The level of the input analog signal Vin is determined by monitoring Di, and the absolute value of the reference voltage supplied to the range control circuit RC, which forms the range control al (N+rc), and the resistance ladder circuit according to the range control signal rc, is determined. A reference voltage switching circuit is provided for stepwise switching.

The quantum resolution of the A/D conversion circuit is changed by switching the voltage value of the reference voltage supplied to the resistance ladder circuit. Therefore, even though the number of installed voltage comparison circuits is fixed and the number of bits of the digital output signal is fixed, the A/D conversion circuit is
According to the level of n, the dynamic range is switched to a predetermined dynamic range according to the stress value of the reference voltage and the voltage difference, and the sensitivity is partially increased.

As shown in the above embodiment, when the present invention is applied to an instantaneous comparison type A/D conversion circuit, the following effects can be obtained. In other words, (1) An instantaneous comparison type This provides the advantage that the dynamic range of the A/D conversion circuit can be arbitrarily set according to the voltage value of the input reference voltage and the voltage difference.

(2) The above +11 term provides the effect that the quantum resolution of the instantaneous comparison type A/D conversion circuit can be partially changed in any level range of the input analog signal, and its sensitivity can be controlled.

(3) The instantaneous comparison type A/D conversion circuit is equipped with a range control circuit that monitors the digital output signal output from the encoder, determines the level of the input analog signal, and forms a range control signal. By changing the voltage value in steps according to the range control signal, the A/D
The effect is that the sensitivity of the conversion circuit can be controlled according to the level of the input analog signal 1'8.

(4) Through the fi1 to (3) above, it is possible to improve the quantum resolution of the instantaneous comparison A/D conversion circuit without increasing the number of voltage comparison circuits installed or the number of points of focus for the digital output signal (and increasing the sensitivity of the instantaneous comparison A/D conversion circuit. The effect is that it can be partially enhanced.

(5) According to the above f11 to (4) terms, instantaneous comparison type A/
It is said that it is possible to improve the performance of digital servo mechanisms, etc., including D conversion circuits, and reduce system costs.
You can get results.

Although the invention made by the present inventor has been specifically explained above based on Examples, it goes without saying that this invention is not limited to the above Examples and can be modified in various ways without departing from the gist thereof. Nor. For example, in Figure 1, the A/D conversion circuit may have three or more dynamic ranges by increasing the number of combinations of reference voltages, or the A/D conversion circuit may have a dynamic range of three or more by increasing the number of combinations of reference voltages. <7 The cleanse does not have to be centered around the zero level. The input analog No. 13 VLn may be input to an L&A/D conversion circuit amplified by a predetermined amplifier circuit, or by changing the amplification factor of this amplifier circuit, the dynamic range of the A/Di conversion circuit can be further validated. The A/D conversion circuit may be configured by combining instantaneous comparison type A/D conversion circuits in series or parallel as shown in FIG. Furthermore, the digital output signal DO-Di may be serially output to other circuit blocks.
Various embodiments may be adopted, such as the specific configuration of the voltage switching circuit, the digitization shown in FIG. 2, and the control method of the -bo mechanism.

In the above explanation, the invention made by the present inventor was mainly explained in the case where it was applied to an A/D conversion circuit used in a digital servo mechanism for an optical disk, which is the field of application that formed the background of the invention, but the invention is limited thereto. For example, the present invention is applicable to various A/D conversion circuits used in various other servo mechanisms, digital control devices, etc. The present invention can be widely used in instantaneous comparison type A/D conversion circuits that instantaneously digitize the level of input analog signals, and in semiconductor devices incorporating such A/D conversion circuits.

〔Effect of the invention〕

A simple explanation of the effects obtained by typical inventions disclosed in this application is as follows. In other words, by supplying input reference voltages from both sides of a resistor ladder circuit that forms a reference potential, and controlling these input reference voltages in stages according to the level of the input analog signal, an instantaneous comparison type A/D conversion circuit can be realized. The quantum resolution of the instantaneous comparison type A/D conversion circuit can be partially improved without increasing the number of installed voltage comparison circuits or the number of bits of the digital output signal. By increasing the sensitivity, it is possible to improve the performance of a digital servo mechanism, etc. including an instantaneous comparison type A/D conversion circuit, and to reduce the cost thereof.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram showing an embodiment of an instantaneous comparison type A/Da conversion circuit to which the present invention is applied. 22 is a signal waveform diagram showing an example of a digital servo mechanism including the A/D conversion circuit of FIG. 1, and FIG. 3 is a circuit block diagram showing an example of a conventional instantaneous comparison type A/D conversion device. It is. A/D...A/D conversion circuit, RC...range control fi
l1 circuit, ENC---x encoder, VC1 to VCn・
...Voltage comparator circuit, Q1-Q4...P channel 84
0SFETSQ5~Q8...N channel MO3FE
T, Nl ・・−(inverter circuit, R1~Rn+l・
··resistance. Representative Patent Attorney Katsuma Ogawa ; Figure 1 Figure 2 c

Claims (1)

[Claims] 1. A resistor ladder circuit comprising a plurality of resistors connected in series and forming a plurality of stepwise reference potentials according to an input reference voltage; a plurality of voltage comparison circuits that commonly receive an input analog signal at the other input terminal; an encoder that receives output signals from the plurality of voltage comparison circuits and forms a digital output signal; and an encoder that receives the digital output signal and forms a digital output signal; A range control circuit that determines that a signal has reached a predetermined level and forms a range control signal, and a reference voltage switching circuit that changes the voltage value of the input reference voltage in steps according to the range control signal, An A/D conversion circuit whose dynamic range is changed according to the level of the input analog signal. 2. The input reference voltage includes a first input reference voltage supplied from one of the resistor ladder circuits and a second input reference voltage supplied from the other resistor ladder circuit, and The A/D conversion circuit according to claim 1, wherein the A/D conversion circuit has a predetermined dynamic range according to the voltage value and voltage difference between the first and second input reference voltages. circuit. 3. The A/D conversion circuit according to claim 1 or 2, wherein the range control signal is output as an output signal of the A/D conversion circuit together with the digital output signal. 4. The A/D conversion circuit according to claim 1, 2 or 3, wherein the A/D conversion circuit is used in a digital servo mechanism.