SU953723A1 - Digital-analogue converter - Google Patents

Description

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The invention relates to a pulse technique and, in particular, to code-voltage converters.

Digital to analog converters are known that contain digital controlled resistances, which are sets of resistive voltage dividers and key elements by the number of bits of the digital code 1 being converted.

The disadvantage of the device lies in its complexity (cfc) due to the need to use a large number of precision resistive and key elements.

A digital-to-analog converter is also known. It contains a reference voltage source and a first switch, the first input of which is connected to the first terminal of the reference voltage source, the second input of which is connected to the second terminal of the source and the first input of the filter, and the output the second input of the smoothing filter, and the digital code converter into a pulse-width signal, the output of which is connected to the control input of the switch 2.

A disadvantage of the known device is the limited accuracy of converting a digital code to a voltage, which is due to the influence, Q of the resistance of the keys and the internal resistance of the source of the reference voltage.

The aim of the invention is to improve the accuracy of the digital-to-analog conversion.

The goal is achieved by first switching to a digital-to-analog converter containing a source of reference voltage. 20, the first input of which is connected to the first terminal of the voltage source, the second input of which is connected to the second terminal and to the point. bearing stress and “go

the smoothing filter, and the output to the second input of the smoothing filter, and a digital converter into a pulse-width signal, the output of which is connected to the control input of the first switch, a second switch, an amplifier with a negative feedback circuit, a voltage follower and a resistor , the first, second and control inputs of the first and second control switches are pairwise combined, the output of the second switch is connected to the non-inverting input of the amplifier, the output of which is connected to the first input of the circuit Yelnia feedback amplifier and via a resistor to the second input of the smoothing filter, the output of which Erez voltage follower coupled to a second circuit yhodom negative feedback amplifier, the inverting input of amplifier circuits connected to the output of negative feedback.

The drawing shows a block diagram of a digital-to-analog converter.

The digital-to-analog converter contains terminals 1 and 2 for connecting a voltage source, switches 3 and, a smoothing filter 5, a digital code converter 6 for a pulse-width signal, an amplifier 7 with a negative feedback circuit 8, a voltage follower 9, . resistor 1 O, output terminals 11 and 12, input terminals 13 for connecting coded signals to be converted to an analog signal. Negative feedback circuit 8 consists of a voltage divider made of resistors and 15. Switches 3 and t inputs are combined and connected to terminals 1 and 2, yp the inputs of switches 3 and connected and connected to the output of converter 6. The output of switch 3 is connected with the input of the smoothing filter 5, the output of which is connected to the output terminals 11 and 12. The output of the switch is connected to the non-inverting input of the amplifier 7. whose output through the resistor 10 is connected to the input of the smoothing filter 5-, -.

Digital-to-analog output. npeoiSprazovatel (terminal 11) through the voltage follower 9 is connected to the output

resistor 15 of the negative feedback circuit 8. The common point of the resistors and 15 is connected to the inverting input of amplifier 7, and the second terminal of resistor 1 is connected to the output of amplifier 7

Digital-to-analog Converter works as follows.

A digital code is applied to the terminals 13 to be converted to an analog signal. Converter 6 converts the input code from terminals 13 into a pulse-width signal that is fed to the control inputs.

5 switches 3 and D. During a pulse-width pulse, switches .3 and synchronously switch to the a position, and during the pause between pulses - to

0 position S..

Rectangular pulses with an amplitude equal to the magnitude of the reference voltage Up and a duration determined by the duration of the output signal of the converter 6, from the output of the switch 3 are fed to the input of the smoothing filter 5 at the output of which is formed directly

equal to

8blX

Jk t eb (X op

t de tyi - pulse duration i transducer 6; T is the period following the impulses of the converter 6,

Since the pulse duration ty (RIGHT is proportional to the input coded signal at terminals 13, therefore, the voltage is am) (at terminals 11 and 12 is proportional to the digital signal at terminals 13.

At the same time, the reference voltage Ion through the switch C, operating synchronously with switch 3, goes to the non-inverting input of amplifier 7 and, after amplification K times through resistor 10, goes to the output of switch 3. The current 1 generated by the voltage source is

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voltage at point b (at the input of the smoothing filter 51; voltage at the output of the smoothing filter 5; resistance value in the circuit of the smoothing filter 5 So as to the inputs of amplifier 7 at the voltage UQI, and Ugj, then the current Ij generated by amplifier 7. where K is the value of the amplification factor of the amplifier 7. The determined value of resistors 1 and 15. - The value of the resistance 10. Find the value of the transfer coefficients of the amplifier 7, which will satisfy the condition UB-U0bix Ki on -Uebix) to ap,) Q TK in case of Uon-iVi «i Jon-UebiK, from where Hence, choosing the value of the transfer coefficient of amplifier 7 by formula (1), it is possible to ensure equality at which the current through switch 3 does not leak. On this switch 3 there is no voltage drop despite the presence of resistance of this switch l. The intrinsic residual voltage of the MOP key is very small and amounts to units of microvolts. In unsteady modes (when the signals at terminals 13 change) when the output voltage of the smoothing filter has both a constant and a variable component, the current 1 also has a variable and a constant component. However, the connection of the output of the filter 5 through the voltage follower 9 to the negative feedback circuit 8 of the amplifier 7 allows to provide exactly the same change in current 1e, i.e. Both the static and dynamic states are equal to 1. CHAMPION OF THE INVENTION A digital-to-analog converter containing a reference voltage source, a first switch, the first input of which is connected to the first terminal of the reference voltage source, the second input of which is connected to the second terminal the reference voltage source and the first input of the smoothing filter, and the output to the second input of the smoothing filter, and the digital code-to-pulse converter, the output of which is connected to the control the first switch, characterized in that, in order to increase accuracy, a second switch, an amplifier with a negative feedback circuit, a voltage repeater and a resistor are introduced into it, the first, second and control inputs of the first and second switches are pairwise combined, the output of the second switch is connected to the non-inverting input of the amplifier, the output of which is connected to the first input of the negative feedback circuit, amplifies the bodies and through a resistor to the second input of the smoothing filter, the output of which ovtoritel voltage coupled to the second input circuit the negative feedback amplifier, the inverting input of amplifier circuits connected to the output of negative feedback. Sources of information taken into account in the examination 1. Semiconductor encoding and decoding voltage converters, ed. V.B. Smolova and. ON. Smirnov. L., Energie, p. 21. fig. 1-6. 2. USSR author's certificate tr, cl. H 03 K 13/20, .06.78 (prototype).

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Claims (1)

The claims where K is the value of the gain of the amplifier 7, the determined value of the resistors 14 and 15; R _<0 - resistance value 10. Find the value of the transfer coefficients of amplifier 7, under which the condition ^ B ^ 0bix K (U _on -U3yx) because when ^υ β ^{= υ} σπ "then ^ op ~ ^and Out Therefore, choosing the value of the gain of the amplifier 7. according to the formula (1), it is possible to ensure the equality 1 _X = 1 ₂ » ^P P ^And which current does not flow through switch 3. In this case, there is no voltage drop on switch 3 despite the presence of resistance of this switch. The intrinsic residual voltage of the MOS key is very small and amounts to units of microvolts. In transient modes (when changing signals at terminals 13)> when the output voltage of the smoothing filter has both constant and alternating components, the current also has alternating and constant components. However, the presence of the connection of the output of the filter 5 through the voltage follower 9 with the negative feedback circuit 8 of the amplifier 7 allows us to provide exactly the same change in current, i.e. how in A digital-to-analog converter containing a reference voltage source, a first switch, the first input of which is connected to the first terminal of the reference voltage source, the second input of which is connected to the second terminal of the reference voltage source, and the first input of the smoothing filter, and the output to the second input a smoothing filter, and a digital code to pulse-width signal converter, the output of which is connected to the control input of the first switch, characterized in that, in order to increase accuracy, it is introduced A second switch, an amplifier with a negative feedback circuit, a voltage follower and a resistor, the first, second and control inputs of the first and second switches are paired, the output of the second 30 switch is connected to a non-inverting input of the amplifier, the output of which is connected to the first input of the negative circuit feedback amplifier., tela and through a resistor with a second input of the smoothing filter, the output of which through a voltage follower is connected to the second input of the negative feedback circuit of the amplifier, in this case, the inverting input of the amplifier is connected to the output of the negative feedback circuit.