JP2007208798A - Digital-to-analog converting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital-to-analog converting apparatus able to be used by connecting a plurality of digital-to-analog converters in a series-parallel manner. <P>SOLUTION: The digital-to-analog converting apparatus is constituted of digital-to-analog conversion portions connected in the series-parallel manner and a general control portion. The digital-to-analog conversion portion is constituted of a semiconductor switch portion to use an input signal as a power source, a filter portion and a pulse modulation control portion. The general control portion is connected to the pulse modulation control portion of each digital-to-analog conversion portion, the whole of the digital-to-analog converters is controlled by the general control portion, and each of the digital-to-analog conversion portions is also controlled by the general control portion. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a digital-to-analog converter that converts a digital signal into an analog signal.

  Conventionally, a control device or the like has often obtained an analog value by combining a plurality of digital information. For this purpose, it is ideal to connect a plurality of digital-to-analog converters in series to obtain an output. Based on this concept, there are many attempts to obtain the composite value of the input to the above-mentioned digital-to-analog converter. Has been done. However, in such a configuration, it is common to input the DA conversion output of the previous stage to the reference power source for DA conversion of the next stage. However, if the output value of the previous stage is small, the accuracy of the DA conversion of the subsequent stage cannot be obtained. As a result, the subsequent digital-to-analog converter required a high-precision DA conversion function.

  Therefore, the internal structure of these digital-analog converters is a combination of constant current circuit and R-2R resistor ladder for the required number of bits, or a constant power source of power of 2 for the number of bits. Therefore, a large number of high-precision resistors are required, the chip size is increased, and depending on the required accuracy, trimming in the state of the chip is also required. It was not possible to use a large number of digital-to-analog converters.

  On the other hand, a high-precision digital-to-analog converter using digital modulation technology and multiple digital input values are calculated using a microprocessor, and these values are input to a single high-precision digital-to-analog converter for analog output. It is also done to get.

  However, in this case, software for operating the microprocessor is required, and further, since the microprocessor and its periphery are necessary, the apparatus becomes expensive and is far from easy to use.

  Therefore, the realization of a digital-analog conversion method that can be used in series-parallel connection and can be used at low cost and a digital-analog converter using this method has been awaited.

JP 2001-069008 A

The present invention solves the conventional problem in the case of connecting a plurality of digital-to-analog converters in series and parallel and outputting a composite value of inputs to each of the digital-to-analog converters,
・ Connect multiple digital-to-analog converters in series and parallel,
・ No need for high precision resistors and trimming,
-To provide a digital-analog converter that can be used easily and can be realized at a low price with a small chip.

  The present invention includes a plurality of digital-analog conversion function units and a general control unit connected in series and parallel. The digital / analog conversion function unit includes a semiconductor switch unit, a filter unit, and a pulse modulation control unit.

  The input signal of the digital / analog conversion function unit is directly connected to the power source of the semiconductor switch unit. The semiconductor switch unit is controlled by a pulse modulation control unit, and its output is connected to a filter unit to constitute a digital / analog conversion function unit.

  The overall control unit is connected to the pulse modulation control unit of each digital / analog conversion function unit, the entire digital / analog converter is controlled by the overall control unit, and each digital / analog conversion function unit is also controlled by the overall control unit. .

By configuring a digital-to-analog converter by connecting multiple digital-to-analog conversion function units in series and parallel under the control of the general control unit,
・ Connect multiple digital-to-analog converters in series and parallel,
・ A digital-analog conversion element and device that can be used easily can be realized.

In addition, by using the control method based on the pulse modulation control unit based on pulse width modulation or pulse modulation for digital-analog conversion, without requiring many high-precision resistors and trimming,
・ Digital-analog conversion elements and devices that can be realized at low cost with a small chip can be realized.

  It is also possible to change individual characteristics by preparing control contents of the pulse modulation control unit for each digital-analog conversion function unit. Of course, it is possible to make the roughness of quantization uniform or to have arbitrary non-linear characteristics, but these are not only set according to the function required in advance, but also include a plurality of characteristics in advance. In addition, it is possible to switch these in accordance with external instructions or preset conditions, and it is possible to realize a digital / analog conversion element or device that can be configured much more flexibly than before. .

As described above, in the digital-analog conversion device of the present invention, by configuring a digital-analog converter by connecting a plurality of digital-analog conversion function units in series and parallel under the control of the overall control unit,
・ Connect multiple digital-to-analog converters in series and parallel,
・ A digital-analog conversion element and device that can be used easily can be realized.

In the present invention, each digital-analog conversion is controlled by pulse modulation.
・ By using standard CMOS logic element technology,
・ Digital-analog conversion elements and devices that can be realized at low cost with a small chip can be realized.

  Furthermore, by individually setting the control contents of the pulse modulation control unit of each digital-analog conversion function unit, it is possible to individually set the characteristics of each digital-analog conversion function unit as necessary. Of course, it is possible to set the roughness of quantization uniformly for each digital-analog conversion function unit, or to set an arbitrary characteristic of non-linearity. Therefore, in the present invention, it is much more flexible than before. A configurable digital-to-analog conversion element or device can be realized.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  FIG. 1 is a schematic diagram of a digital-to-analog converter using the present invention.

  The digital-analog converter 10 includes digital-analog conversion function units (1, 2, 3, 1,..., 3.n) connected in series and parallel and an overall control unit 4. Each digital / analog conversion function unit includes a switch unit (1, 1, 2, 1, 3, 1, 1,..., 3 · 1, n) and a filter unit (1, 2, 2, 2, 3, 2, 1... 3 · 2 · n) and a pulse modulation control unit (1,3,2,3,3,3,1, ... 3 · 3 · n).

  The input signals (1, 4, 2, 4, 3, 4) of the digital-analog conversion function units (1, 2, 3, 1,..., N) are connected to the switch units (1, 1, 2, 1, 3, 3).・ 1 ・ 1, ... 3 ・ 1 ・ n) Connected to the power supply, and the output of each switch unit is connected to the filter unit (1,2,2,2,3 ・ 2,1, ... 3 ・ 2 ・ n) Has been. Each switch unit (1, 1, 2, 1, 3, 1, 1, ... 3 · 1 · n) is connected to a pulse modulation control unit (1, 3, 2, 3, 3, 3, 1, 3). 3 · n), each digital / analog conversion function section (1, 2, 3, 1,... 3 · n) is configured.

  The input of the first-stage digital / analog conversion function unit 1 is connected to the reference power supply 7, and the subsequent-stage digital / analog conversion function unit input is connected to the output of the previous stage of the digital-analog conversion function unit.

  The pulse modulation control units (1, 3, 2, 3, 3, 3, 1, ... 3, 3, n) of each digital / analog conversion function unit are controlled by the overall control unit 4, and the digital / analog converter 10 is also configured. It is controlled by the overall control unit 4.

  The digital-to-analog converter 10 is connected to the external interface 6 via the external interface control unit 5 and enables an instruction from the outside.

  The digital-analog conversion function units 1 and 2 constitute a series assembly, and the output of the first conversion function unit 1, that is, the output of the filters 1 and 2, is the input of the second conversion function unit 2, that is, the switch unit 2 1 and the output of the filters 2 and 2 of the second conversion function unit 2 becomes the output of the series assembly (1, 2).

  On the other hand, the digital / analog conversion function units 3... 3 · n constitute a parallel assembly. The input of each conversion function part which comprises a parallel assembly is common, and is an output of filter 2 * 2 in an Example. The output of the parallel assembly is the output of each conversion function unit, that is, the output of the filters 3 · 2 · 1 to 3 · 2 · n.

  In the embodiment of FIG. 1, a configuration in which parallel assemblies (3 · 1... 3 · n) are connected to outputs of the series assemblies (1, 2) is illustrated. The combination of the serial assembly and the parallel assembly is arbitrary. For example, the input of the serial assembly or a single digital-analog conversion function unit is connected to one of the outputs of the parallel assembly, or one parallel assembly 3 shown in FIG. It is also possible to connect the input of another series assembly to one output.

  The configuration of FIG. 1 can be used as, for example, an LED driving driver for a liquid crystal backlight. The overall brightness is controlled by the conversion function unit 1 in the first stage, and the gradation is controlled by the following 2. Furthermore, each color (R, G, B) can be controlled by 3 · 1 · 3 · n.

  FIG. 2 shows details of the digital-analog conversion function unit.

  The switch unit 21 is composed of a P-channel MOSFET 21 • 1 and an N-channel MOSFET 21 • 2 as in a normal CMOS logic circuit, and the source of the P-channel MOSFET is connected to an input signal 25 which is a power source. The source of the N-channel MOSFET is connected to 0V. In addition, the drains of the MOSFETs are connected to each other to be the output of the switch unit 21, and the gates of the MOSFETs are connected to each other to be the input to the switch unit 21. This circuit is generally called a CMOS logic circuit. It is the same as the logic circuit.

  The switch unit 21 is controlled by a pulse modulation control unit 22. The pulse modulation control unit 22 includes a pulse modulation unit 22.1, a decoding unit 22.2, and a DA conversion value setting register 22.3. The operation is based on the pulse signal generator 24 input from the outside.

  Based on the information set in the DA conversion value setting register 22.3 via the external interface control unit 5 from outside, the decoding unit 22.2 analyzes the information and generates a setting value for pulse modulation. In accordance with the information, the pulse modulation unit 22.1 controls the switch unit 21.

  The pulse modulation here refers to pulse width modulation (PWM) for changing the pulse width, pulse number modulation (PNM) for changing the pulse period, or a pulse modulation method based on these. .

  Further, in order to obtain a desired output from these pulse-modulated signals, it is necessary to remove the frequency used for the pulse modulation, and for this purpose, a filter (filter) is required.

  The filter unit 23 having a filtering function for removing an unnecessary signal from the output of the switch unit 21 includes an operational amplifier 23. 1 and a peripheral circuit element group 23. 3 including a resistor, a capacitor, and the like. The filter unit 23 includes switches 23 and 2 for switching the value of the feedback resistor in accordance with an instruction from the decoding unit 22 and changes the output voltage value of the filter unit 23 within a preset range. It has a function to make it.

  Note that the switch unit 21 can operate in a relatively wide voltage range, but the operating voltage range is limited. Therefore, when the setting information in the DA conversion value setting registers 22 and 3 is out of the preset range so that the output voltage of the switch unit is within the normal operation range of the next-stage switch unit, the information The decoding unit 22.2 operates the switch unit by using a value obtained by multiplying the value by a constant set in advance, and when the setting information is within a preset range, the information is used as it is. In addition to giving an instruction, the information is also sent 26 to the overall control unit 4. Further, in the digital / analog conversion function section at the final stage, the overall control section 4 outputs the value obtained by dividing all the multipliers multiplied before the conversion function section by the synthesized value. An instruction 27 is given to the decoding unit.

To adjust the output voltage in the digital-analog conversion function section,
The value of the feedback resistor is switched by the filter unit 23.
Processing is performed in advance so that the output becomes a predetermined value in the pulse modulation unit and decoding unit.
However, any method may be used.

  These operations will be described with reference to FIG.

  When the DA conversion instruction information is represented on the horizontal axis and the output voltage after DA conversion is represented on the vertical axis, the ideal should be the straight line 31 extending diagonally from the origin to the upper right side, here indicated by a broken line. If the DA conversion instruction information is small because the operating voltage of the unit is limited, the value on the curve indicated by the alternate long and short dash line 32 is output. In order to prevent this, in the present invention, DA conversion is once performed with a value obtained by multiplying the DA conversion instruction information by a preset value such as 2 or 4 so that the output is in the range of the maximum value 34 and the operation lower limit voltage 35. I do. The output at this time is a sawtooth waveform 33 -indicated here by a bold line-on the value above.

  This operation is repeated in each digital / analog conversion function unit, and in the final stage, a value obtained by dividing the coefficient multiplied in the previous stage is output by each digital / analog conversion function unit, whereby a straight line 31 extending diagonally from the ideal origin to the upper right. You can get the above value.

1 schematically illustrates a digital-to-analog converter according to the present invention. It is a figure which shows the detail of a digital analog conversion function part. It is explanatory drawing of an operation waveform.

Explanation of symbols

1, 2, 3, 1, ... 3, n Digital-analog conversion function unit 1, 1, 2, 1, 3, 1, 1, ... 3, 1, n Switch unit 1, 2, 2, 2, 3, 2 ······························· 2 · n Filter part 1 · 3 · 2, · 3 · 3 · 3 · 1, ... 4 General control unit 5 External interface control unit 6 External interface 7 Reference power supply 10 Digital-analog converter 21 Switch unit 21.1 P-channel MOSFET
21.2 N-channel MOSFET
22 Pulse modulation control unit 22.1 Pulse modulation unit 22.2 Decoding (decoding) unit 22.3 DA conversion value setting register 23 Filter unit 23.1 Operational amplifier 22.3 Switch 23.3 Peripheral circuit element group 24 Pulse signal generation 25 Input signal 26 Sending information 27 Instruction 31 DA conversion ideal output straight line 32 DA conversion actual output 33 Waveform 34 Maximum value 35 Operating lower limit voltage

Claims (4)

  A plurality of digital-analog conversion function units each having a pulse modulation control unit, a semiconductor switch unit that switches an input signal in accordance with the control of the pulse modulation control, and a filter unit that is connected to the output of the semiconductor switch unit and outputs an analog signal In addition, the digital / analog conversion function units are connected in series or parallel to each other to form a series assembly or parallel assembly, and the assembly or a single digital / analog conversion function unit is connected in series or in parallel. Digital-analog converter.   In contrast to the first aspect, an amplification function with a fixed or variable amplification is added between the input of the at least one digital-analog conversion function section and the semiconductor switch section and one or both of the filter sections. A digital-to-analog converter characterized by changing the amplification degree in accordance with preset contents or in accordance with an external instruction when is variable.   Each digital-analog conversion function unit is connected to each digital-analog conversion function unit, and an overall control unit that controls the entire digital-analog converter is provided, and the overall control unit is set according to preset contents or by an external instruction signal In addition to outputting a multiplication value of a preset value so that each digital / analog conversion function unit output is an output within a predetermined range, the last-stage digital / analog conversion function unit The digital-to-analog converter according to claim 1, further comprising a function of performing division by the performed multiplication value. Each digital / analog conversion function unit, general control unit, or any part of it has a plurality of digital / analog conversion gradation controls, which can be switched according to preset contents or according to an external instruction signal. The digital-to-analog converter according to any one of claims 1, 2, and 3, characterized in that

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