RU74022U1 - DEVICE FOR NONLINEAR DIGITAL ANALOG CONVERSION OF A SIGNAL - Google Patents

Abstract

The utility model relates to the field of radio engineering, telecommunications, information-measuring equipment and can be used for non-linear digital-to-analog signal conversion. The functional digital-to-analog signal conversion device is based on non-linear polynomial conversion of the original signal, in which the original digital signal is subjected to digital-to-analog conversion using n digital-to-analog converters of the multiplying type. The output voltages of the digital-to-analog converters and the reference voltage are summed with the corresponding transfer factors. The coefficients are set using digital-controlled linear scale converters. The changes in the coefficients are provided by the joint operation of the interface device, registers, and corresponding digital-controlled linear scale converters. The technical result achieved is the expansion of the set of transformation functions to a class of elementary functions with the ability to configure to implement any of them.

Description

The inventive device for non-linear digital-to-analog signal conversion relates to the field of radio engineering, telecommunications, information-measuring equipment (in particular, phase calibrators) and can be used for non-linear digital-to-analog signal conversion.

For nonlinear digital-to-analog conversion, various resistor arrays can be used, in which the resistors are selected according to special laws [1, 2]. However, the use of such non-linear converters is limited to the implementation of only one conversion characteristic.

A device and method for constructing functional digital-to-analog converters (DACs) based on a piecewise-linear approximation of the required functional dependence [3]. The digital-to-analog signal conversion device includes an N-bit digital input, a decoder, and a linear DAC. The digital code N arriving at such a device is divided into two parts, the high-order bits being used by a decoder to select the maximum and minimum voltages of a given linear section of the approximation and fed to the linear DAC, which controls the low-order bits of the digital code and forms this section.

The accuracy of the devices providing piecewise linear approximation will depend on the choice of the method of dividing the approximated curve into linear sections. But even with the optimal choice, the error in the reproduction of the function may turn out to be unsatisfactory.

To increase the accuracy, it is advisable to use the approximation of the necessary functional dependence of the polynomial or quotient of two polynomials. The approximation errors are significantly reduced.

Fractional rational approximation is used in functional converters, consisting of multiplying DACs, to which a digital code is supplied, operational amplifiers (op amps), passive voltage dividers and resistors [4]. The output voltage of the device depends on the input digital code as a fractional rational function R (N)

Using the methods of the mathematical apparatus, the required transformation function is determined in a fractionally rational form and the coefficients of the function R (N) are found, which are set using resistors and passive dividers.

A significant drawback of such a device is the invariability of the transfer characteristic, which is set when constructing the Converter, due to the connected coefficients of the rational fraction. it

severely limits the capabilities of systems and devices built using this type of functional converters. It should be noted that these converters are not able to work with a digital code that has a signed bit.

The implementation of a power function of degree n is possible with the help of n multiplying DACs, switched on so that the reference voltage is applied to the analog input of the first of them, and the output voltage of the previous DAC is supplied to the analog inputs of each subsequent DAC [5]. In this case, at the output of each i-th DAC, a voltage is generated proportional to the degree i of the supplied code.

Such a device has the disadvantage of being able to carry out only a certain set of functions (power functions) and does not have the ability to reconfigure. Obviously, the multiplication of the obtained stresses by certain coefficients, followed by addition, will make it possible to apply a power-law approximation.

The prototype of the utility model is a device for broadband frequency and phase multiplication, which contains n digital-to-analog converters of the multiplying type, while the analog input of the first digital-to-analog converter is connected to the output of the constant reference voltage source, and the analog input of each of the n-1 subsequent digital-to-analog converters is connected to the analog output of the previous one D / A converter, each of the analog outputs of the D / A

converters and the output of the reference voltage source through the corresponding linear scale converters with the specified transmission magnitude and sign are connected to n + 1 inputs of the analog adder, the output of which is connected through the low-pass filter to the output of the device [6].

The disadvantage of the prototype device is that the change in the reference voltage and voltage from the analog outputs of the DAC is made at constant coefficients. This is justified in terms of frequency and phase multiplication, but significantly limits the scope.

The task is to expand the set of conversion functions to a class of elementary functions with the ability to configure to play any of them.

To do this, in a known device based on non-linear polynomial conversion of the original signal, and consisting of n digital-to-analog converters of the multiplying type, the analog input of the first digital-to-analog converter is connected to the output of the constant reference voltage source, and the analog input of each of n-1 subsequent digital-to-analog converters connected to the analog output of the previous digital-to-analog converter, each of the analog outputs of the digital-to-analog converters and the output is reference voltage reference through the corresponding linear scale converters with the specified magnitude and sign of the transmission coefficients are connected

with the corresponding inputs of the analog adder, the output of which is connected through the low-pass filter to the output of the device, the digital inputs of the digital-to-analog converters are connected to the information digital input of the device, and all linear scale converters are digital-controlled, each of which has digital inputs connected to the corresponding digital outputs of one of the n + 1 additionally entered registers in which a digital code is written that determines the transmission coefficients in the corresponding large-scale programs at the same time, the registers with inputs of “write permission” and digital inputs are connected to the corresponding outputs of the interface device, the inputs of which are connected to the control digital input of the device using the standard data exchange interface.

Thus, a useful model of the device allows you to get a new technical effect - to expand the set of conversion functions to a class of elementary functions with the ability to configure to play any of them by changing the transmission coefficients determined by the code recorded in the corresponding registers using the interface device according to certain laws.

The application of the proposed device in comparison with the known allows to obtain any elementary function f (N) as a conversion function. Indeed, the sum of the output voltage of the DAC and the reference voltage obtained at the output of the adder is the voltage

proportional to the polynomial P _n (N) of degree n. The coefficients of the polynomial P _n (N) are calculated so that on the selected interval for changing the digital code N, the condition

where ε is the approximation error, and is set during programming of the device by writing the corresponding data to the registers. The fulfillment of condition (1) is possible for any elementary functions. The minimum value of ε will depend on the form of the function f (N).

The drawing shows a functional digital-to-analog signal conversion device.

The device contains n multiplying digital-to-analog converters 1-4, each bit of the digital input of which is connected to the corresponding digital bit of the information input 5 of the device. The analog input of the first DAC 1 is connected to the output of the reference voltage source 6. The analog input of each of the n-1 subsequent DACs is connected to the analog output of the previous DAC. In addition, the output of the reference voltage source 6 through a digitally-controlled linear scale converter 7 with a set transfer coefficient a ₀ and the analog output of each i-DAC through the corresponding digital-controlled linear scalers 8 - 11 with set transfer factors a _{i are} connected to the inputs of the analog adder 12. The digital inputs of the converters 7-11 are connected to the digital outputs of the respective

registers 13-17. Registers 13-17 their digital inputs are connected to the data outputs of the device 18 interface. The “write enable” input of each of the registers 13-17 is connected to one of the address outputs of the interface device 18 (these connections are not shown in the drawing). The input of the interface device 18 is the control input 19 of the functional DAC, which is connected to a bus using a standard communication interface (for example, ISA). The output of the adder 12 through the low-pass filter 20 is connected to the output 21 of the functional DAC.

The device operates as follows.

Before the device starts, it is configured for the necessary conversion function. For each of the registers 13-17 alternately at the control input 19 set its address and data. For the i-th register 13-17, the control digital code is the data in which the transfer coefficient of the i-th scale converter 7-11 is a _i . The device 18 interface at the address received from the control input 19, selects the corresponding register 13-17 and writes data to it.

The information digital code N (t) from input 5 is fed to the digital inputs n of the DAC 1-4, which perform the function of potentiometers controlled by a digital code. The instantaneous voltage value at the output of the first DAC 1 is

where b is a conversion constant of each DAC 1-4. At the output of each i-th DAC 1-4 account, the instantaneous voltage U _i will be equal to

The output of the adder 12 voltage U _Σ (t) is equal to

The values of the transmission coefficients a _{i are} calculated in accordance with the value of b and condition (1). In this case, after passing through the low-pass filter 20 at the device output 21, we obtain a voltage proportional to the function f (N (t)) of the information code N (t) supplied to the input of the functional DAC.

Information sources:

1. Non-linear digital-to-analog converter for servo circuit. (Non-linear digital-to-analog converter for drives) US Patent MKI N03K 13/04 No. 4020485, 04/26/1977.

2. Non-linear type digital-to-analog converter. (Digital-to-analog converter of nonlinear type) US Patent MKI N03K 13/02 No. 4062013, 12/06/1977.

3. Non-linear digital-to-analog converter and display incorporating the same. (Nonlinear digital-to-analog converter and display containing it) US Patent MKI N03K 13/02 No. 6154121, 11.28.2000.

4. Electronics: Reference book / Ed. Yu.A. Bystrova. -SPb .: Energoatomizdat, 1996., p. 243-245.

5. Gnatek Yu.R. Handbook of digital-to-analog and analog-to-digital converters: Per. from English / Ed. Yu.R. Ryuzhina. - M .: Radio and communications, 1982. S.259-260, Fig. 4.129-4.130.

6. A method of broadband frequency and phase multiplication and a device for its implementation. Patent of the Russian Federation Н03В 19/10 No. 2186454 C2 07/27/2002. (prototype).

Claims (1)

A functional digital-to-analog converter based on non-linear polynomial conversion of the original signal and consisting of n digital-to-analog converters of the multiplying type, while the analog input of the first digital-to-analog converter is connected to the output of the constant reference voltage source, and the analog input of each of the n-1 subsequent digital-to-analog converters is connected to the analog output previous digital to analog converter, each of the analog outputs of the digital to analog converter th and the output of the reference voltage source through the corresponding linear scale converters with the specified transmission magnitude and sign are connected to the corresponding inputs of the analog adder, the output of which through the low-pass filter is connected to the output of the device, characterized in that the digital inputs of the digital-to-analog converters are connected to the information digital input devices, and all linear scale converters are digitally controlled, with each of them connected to digital inputs to the corresponding digital outputs of one of n + 1 additionally entered registers, which are “write enable” inputs and digital inputs are connected to the corresponding outputs of the interface device, the inputs of which are connected to the control digital input of the device using the standard data exchange interface.