JPH07297723A - DAC dynamic range conversion circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] D / A conversion (DAC) when input signals are a plurality of signals each having a different number of bits, so that the entire dynamic range is used for any input signal. . [Structure] Digital data composed of N bits,
In a circuit for converting a plurality of digital data composed of an arbitrary number of bits less than the same N bits as an input signal and converting each of the digital data into an analog signal,
Digital data D with any number of bits less than bits
Data converters 1 and 2 provided for each digital input signal for converting 1 and D2 into the same N-bit digital data
An N-bit selector 3 for switching between the N-bit digital data D3 and the digital data from each of the data converters, and a D / A for converting the N-bit digital data from the N-bit selector into an analog signal. It is composed of the converter 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DAC dynamic range conversion circuit, and more particularly to a DAC dynamic range conversion circuit in the case where the input signals are a plurality of signals each having a different number of bits. The present invention relates to a dynamic range conversion circuit adapted to operate in a range.

[0002]

2. Description of the Related Art When a plurality of digital data having different bit numbers are analog-converted by a single DAC (digital-analog converter), conventionally, a signal having the bit number is converted into an analog signal.
Now, let us consider a case where the plurality of digital data are video signals, the maximum number of bits of the plurality of digital data is 8 bits, and the DAC is also for the same 8 bits. The maximum value of the 8-bit video signal is "255" [(2 to the 8th power) -1 = 255]. Therefore, the DAC output for this signal has a level corresponding to "255", which is the maximum amplitude of the video signal. On the other hand, when a 4-bit video signal is converted into an analog signal by the 8-bit DAC, its maximum amplitude remains at the level of "240". This is because, since it is 4 bits, [(2 to the 4th power) -1 = 15] is lower than the case of 8 bits.

Therefore, the analog output at the maximum amplitude has the following relationship between the 8-bit video signal and the 4-bit video signal. 240/255 = 0.94 (= 94%) That is, the level of a 4-bit video signal is 6% lower than that of an 8-bit video signal. Furthermore, considering the gamma characteristics of the monitor (gamma correction coefficient is 2.2), the brightness has the following relationship. (240 to the power of 2.2) / (255 to the power of 2.2) = 0.88 (= 88%) In other words, the brightness on the monitor is reduced by 12% (darkened). The conventional analog conversion has the above-mentioned drawbacks as a result of not using the entire dynamic range of the DAC in a signal having a small number of bits.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional drawbacks, and a plurality of digital signals having different numbers of bits are combined into one DAC.
It is an object of the present invention to provide a conversion circuit adapted to convert any digital signal by using the entire dynamic range of the DAC when analog conversion is performed.

[0005]

According to the present invention, an input signal is digital data composed of N bits and a plurality of digital data composed of an arbitrary number of bits smaller than the N bits, and each of the digital data is input. In a circuit for converting into an analog signal, a data conversion unit provided for each digital input signal for converting digital data of an arbitrary number of bits less than N bits into the same N-bit digital data, and the N-bit digital data. ,
A DAC dynamic range conversion circuit configured by an N-bit selector for switching digital data from each of the data conversion units and a D / A converter for converting N-bit digital data from the N-bit selector into an analog signal. It is provided.

[0006]

The maximum number of bits of a plurality of digital data is N. The digital data having a bit number smaller than N is converted into an N-bit signal by a data conversion unit (bit number conversion) provided corresponding to each signal. The conversion into the N-bit string is performed by a ROM in which a conversion table is written, or a method of multiplying a predetermined multiplier by a multiplier. The conversion processing by the above method is not necessary for N-bit digital data. The data converted into N bits by each bit conversion circuit and the originally N bit signal are switched by the N bit selector. The N-bit data from the selector is converted into an analog signal by the N-bit DAC.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A DAC dynamic range conversion circuit according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an essential part showing an embodiment of a DAC dynamic range conversion circuit according to the present invention, which is an example in the case where input digital data is changed from a 4-bit signal to an 8-bit signal, and FIG. FIG. 3 is an explanatory view of data conversion for explaining FIG. 1, and FIG. 3 is a block diagram of essential parts showing another embodiment of the DAC dynamic range conversion circuit according to the present invention. FIG. 1 shows an embodiment in which data conversion is performed based on a look-up table (LUT). D1 is 4-bit digital data, D2 is 5-bit digital data, D3 is 8-bit digital data, and 1 is a predetermined value. A look-up table 1a is provided, and a data conversion section 2 for converting 4-bit digital data D1 into 8-bit digital data is provided with a predetermined look-up table (not shown) like the conversion section 1. Is provided, 3 is a data conversion unit for converting digital data D2 of 5 bit configuration into digital data of 8 bit configuration, 3 is an 8-bit selector for signal selection, and 4 is an analog of the digital data selected by the selector 3. 8-bit D converted to a signal
AC (digital-analog converter) and Ao are converted analog signal outputs.

FIG. 2 shows an embodiment in which data is converted by a multiplier. The same components as those in FIG. 1 are designated by the same reference numerals, and 11 is provided with a predetermined multiplier 11a and has a 4-bit structure. The data conversion unit for converting the digital data D1 of the above into the digital data of the 8-bit structure, 12 is provided with a predetermined multiplier (not shown) like the conversion unit 1, and the digital data D2 of the 5-bit structure is converted into It is a data conversion unit for converting digital data having an 8-bit structure. Note that FIG.
Also, in FIG. 2, 6-bit and 7-bit data are omitted.

Next, the operation of the present invention will be described. As shown in FIG. 1, the maximum number of bits in the input data is 8
If it is a bit, data D1 other than D3 (8 bits)
A required number of data conversion units such as data conversion units 1 and 2 for converting data into 8-bit strings are provided on lines such as (4 bits) and D2 (5 bits), and data conversion is performed respectively. Here, the maximum number of bits of a plurality of data strings to be handled is n
(8 in this embodiment), the maximum value of the data is as follows. Maximum value = [(2 to the nth power) −1] (1) On the other hand, if the number of bits of the data string to be converted is m (4 and 5 in this embodiment), the maximum value of the data is Becomes Maximum value = [(m to the power of 2) −1] (2) Therefore, if the value of the m-bit data string (before conversion) is X and the value of the n-bit data string (after conversion) is Y, The relationship between Y and X can be expressed as follows using the above equations (1) and (2). Y = X. [(2 to the nth power) -1] / [(2 to the mth power) -1] ... (3) A specific method example of the conversion according to the above equation (3) is shown below.

(1) Method of converting by a memory (ROM or the like) in which the conversion table is written For example, when converting D1 (4 bit string) into 8 bits, n = 8 and m = 4. ) The formula is as follows. Y = X · 255/15 (4) A conversion table [lookup table (LUT) 1a] in which X in the equation (3) or (4) is an address and the conversion data corresponding to the address is Y A written memory (ROM or the like) is provided to convert data. Figure 2
Is a correlation diagram of 4-bit string data D1 and 8-bit string data. The above conversion is performed under the relationship shown in FIG. 2, where the left column (input) is the address X and the right column (output) is the output Y.
Becomes For the other bits D2, etc., an LUT based on the same method as above is provided and converted into 8-bit data.

(2) Method of Multiplying a Predetermined Multiplier by a Multiplier to Convert FIG. 3 is a principle block diagram showing a method of converting by a multiplier. As shown in the figure, a predetermined multiplier 11a is provided for each input data line (data converters 11 and 12), and the multipliers multiply the input (X) such as D1 or D2 based on a required multiplier, Convert to required output data Y (= kX). The multiplier k in this case is set to the value shown in the figure. The above is the method of converting m-bit string data (D1 or D2) in the data converters 1, 2, 11, 12 and the like into n-bit string data. The data converted into an 8-bit string in this way is 8
It is sent to the bit selector 3. The data D3 of which the original data is an 8-bit string is directly input to the selector 3. The selector 3 selects the required data, and the 8-bit DAC 4 converts the selected data from digital data into an analog signal Ao. Since all data input to the same DAC 4 is an 8-bit string, analog conversion is performed in the entire dynamic range of the same DAC 4. As a result, the entire dynamic range of the DAC 4 is effectively used.

[0012]

As described above, according to the present invention, it is possible to convert all of a plurality of digital signals having different bit numbers into a signal sequence having the same number of bits as the signal having the maximum number of bits and performing analog conversion. it can. As a result, any digital data is converted into an analog signal by using the entire range of the DAC dynamic range, and it is possible to obtain a sufficient maximum amplitude even for data having a small number of bits. Therefore, the image quality of a monitor or the like can be improved by implementing the present invention.

[Brief description of drawings]

FIG. 1 is a principal block diagram showing an embodiment of a DAC dynamic range conversion circuit according to the present invention.

2 is an explanatory diagram of data conversion for explaining FIG. 1. FIG.

FIG. 3 is a principal block diagram showing another embodiment of the DAC dynamic range conversion circuit according to the present invention.

[Explanation of symbols]

 1 4-bit to 8-bit data conversion unit 11a Look-up table (LUT) 2 5-bit to 8-bit data conversion unit 3 8-bit selector 4 8-bit DAC D1 4-bit data D2 5-bit data D3 8-bit data Ao conversion analog signal 11 4-bit to 8-bit data converter 11a Multiplier 12 5-bit to 8-bit data converter

Claims (3)

[Claims] 1. A circuit for converting digital data composed of N bits and a plurality of digital data composed of an arbitrary number of bits smaller than the N bits as input signals and converting each of the digital data into an analog signal. A data conversion unit provided for each digital input signal for converting digital data of an arbitrary number of bits less than N bits into digital data of the same N bits;
An N-bit selector for switching between bit digital data and digital data from each of the data conversion units, and a D / A converter for converting the N-bit digital data from the N-bit selector into an analog signal. A DAC dynamic range conversion circuit characterized by the above. 2. The data conversion in each of the data conversion units is provided with a memory unit that stores the converted data as an address and the N-bit conversion data corresponding to the address as a conversion table. 2. The DAC dynamic range conversion circuit according to claim 1, wherein the converted data is converted into N-bit data based on the conversion target data. 3. In the data conversion in each of the data conversion units, a multiplier is provided for each data to be converted, and the data to be converted is multiplied by a required multiplier of the multiplier to convert it into N-bit data. The DAC dynamic range conversion circuit according to claim 1, wherein