IL32703A - Digital-analogue converter with bipolar output - Google Patents

Description

i 0101 TAL-ANA OOUE CONVERTER WI TH BIPOLAR OUTPUT nna in PIT The present invention relates to "apparatus for the conversion of digital signals into positive and negative values of current or voltage, respectively, the said apparatus being one with pulse-code-modulation* Such systems have also become known under the designation "digital - analogue ~ converter"!, wherein in a first step there is formed a code word to each bit of which is coordinated the value of voltage or current, and then, in a second step, these coordinated values are added up and are possibly converted into a voltage.

For realizing the first step a number of voltage or current souroes are required»the initial values of which are at a predetermined relation to one another, ' say they form a binary row. There are\also required switches which, are controlled, by, lihe code oi^ o select initial values, and for the realization of the second . step, feed these initial values to an adding system which combines them into one value and creates in a known .manner one single effective voltage.

The voltages or current values are frequently created with so-called weight sets* These are resistor networks where from constant voltages and constant currents, there can be obtained,partial currents, the magnitudes of whioh are at a predetermined relation to one another* Generally voltages or currents are connected only with one polarity and yield so-called unlpplar analogue si nals* From the uni olar analo ue si nals bi olar analo u signals are obtained by means of amplifiers (whioh vtere necessary invert the polarity of the signal).. This is an operation which requires an undesirably large installation* It is the object of the inventio to provide an analogue-digital-oonveyter by means of which bipolar analogue signals are produced directly..

The invention is characterized thereby that for the reception of the code words there is provided a shift register, and that the conversion occurs in a resistor network which is composed of a line of resistors connected in series and cross resistors conneoted between She first named resistors, and in which arrangement the free connection of each cross resistor is connected via an electronic switch to a positive and a negative source of current, as well as to earth, and that furthermore to each storage, element of the shift register is coordinated one of the cross resistors, and that to each of the groups so formed is coordinated a switch oontrol for operating at least one switch of the group on the basis of the contents of the shift register and the polarity information* ' , · .. ' ■ The invention will now be explained with the aid of one practical example; show in the annexed drawings.

The system for conversion is a five digital channel netxiork having junction points, EL,B2,B3,B4 and B5. The output from the channel network is connected via an inverse feed-back amplifier to 1the output A, whioh amplifier h e i or RC.

The channel network ie formed by a number of resistors R arranged in series in a row, all of the same resistance value* At the points of connection of the junction points Bl to B5 of the channel network, there are provided cross resistors 2R which also have the same resistance values. At the ends of the channel network there are oonnected compensation resistors.

At the first junction point Bl there is connected, a coupling resistor RA, and at the last junction point B5 a load resistor RL, which are both a earth potential.

The bases of the cross resistors 2R are each connected to three electronic switches, SI to 315. The first one of, these groups of three switohes is connected tqa positive pole of a source of constant circuit, the second on© of these groups is connected to a negative pole of a souroe of constan current, while the third is connected to earth. For electronic switches there are provided field-effect-transistors FET. The control of these switches occurs via a switch control according to the word received. This consists, for each group of three switches, of two AND gates with inverted outputs Ul to UIO to which Is connected in pairs the information of one polarity bit and the information from the code word. The output from each of these gates Ul to UIO Is oonnected to a first and to a second electronic switch S , 32, and so on, while each "th^d electronic switoh S3 receives directly the information of the code word.

V a shift tap at the input ST, the code word is introduced into the shift register SR. By means of an output terminal UT the contents of the shift register are fed in parallel into a storer which is composed of storage cells SZl to SZ6. At the output Q from these storage cells SZl to SZ6 there appears for a logical !" in tho/6ode word also a logical ,"1", At the storage cell SZ6 which contains the polarity information, there appears additionally at the output "Q a logical "1" for a logical "O" in the code word., To each of the above mentioned gates Ul to UIO of the switch control there are fed the information from the storage cell SZl to SZ5 for the identification of the amplltt¾e value, and, the Information from the storage cell SZ6 for the polarity* This occurs in such manner that each o the first named storage cells SZl to SZ5 controls two gates thereof, one being connected to the output Q, and the other being connected . to the .output 3f/ of the storage cell SZ6, The switchin control and the electronic switches operate in such manner that with a logical "1", the electronic switches interrup the voltage to the base, i.e.* the switches are open; and only with a logical "O" is the voltage connected. to the base, i.e. » the switches are closed* In this event, the switch control always closes only one electronic switch of a group of three* If for instance the condition of a bit stored in a storage cell SZl is that of a logical "0" the electronic a logical "lw independently from the polarity information. The baseof the channel network is connected to earth by means of the electronic switch S3. On the other hand,' when the storage cell SZ1 has stored a logical "1", this is ed directly to electronic switoh S3, At the output of gate Ul there appears a logioal "0" due to inversion at positive polarity; that is to say, there is a logical "1" at the output Q and a logical "O at the output :Qi: of the memor cell SZ6| At the same time the output of gate U2 shows a logical "1% This results in that only the electronic switch SI closes, and the two other electronic switches S2 and S3 remain open. Thus the respective base of the channel network receives a positive voltage.

With a stored logioal "1" in the storage cell SZ1 and with negative polarity, that is to say, with a logical "O" at the output Q and with a logioal nlw at the output Q», the output of gate Ul presents a logioal "1" due to the inversion? and the output of gate U2 presents a logioal "0" also due to inversion. The result is that by means of the electronic switch S2 the negative voltage is applied to the base point, At every base point of the network there is applied, according to the code word, either earth or positive or negative voltage, respectively. Every base point to which is applied a positive or negative voltage, respectively, supplies current at the output junction point B5 of the network, which is at predetermined relation to the respective base point. Due to the resistor network which V voltage at every further base point supplies each time a partial-current which is higher by the faotor 2 as against the preceeding base point at the output junction point B5.

Thus at this output -Junction point B5 there appears a total current which is equivalent to the received code word* The polarity of this total current is directly controlled by the polarity information from the respective positive or negative voltage. In the inverse feedback amplifier OA* the total current is then converted into a voltage, which appears at the output A. To serve as positive and negative voltages which are connected via the switches SI to S15 to the network, there are provided regulated voltages* the positive voltage value and the negative voltage value being positioned symmetrically to the earth potential* In the above example there has been described a converter for a code word with five bits, For a pulse-code system, wherei the fed-ln signal is transmitted to in compressed form/be again expanded at the receiver, it would be necessary to insert, between the shift register SR and the shift storer, SZ1 to SZ6, a compander logic. It goes without saying that the network has to have as many junction poihts as there are digital positions for the representation of the amplitude value prior to companding.

The network shown forms a binary row and thus it is intended for binary codes. For a ternary code it would be neoessary to form a ternary row.

Claims (1)

1. 2. P.A. 327O3/II 3. Apparatus, as claimed in Claim 1, characterized thereby that the switch control in eac& g oup switches each time an electronic switch into conductivity, and tuo electronic snitches into non-conductivity. 4. Apparatus as claimed in Claim 1, characterized -7a thereby that as electronic switches there are used field-effect transistors wherein the source electrode is connected to the source of curren , and the drain electrode to the cross resistor of the resistor network, the gate electrode being controlled by the control of the switches. 5. Apparatus as claimed in Claim 1, characterized thereby that the switch control is a logical element, 6. Apparatus as claimed in Claim 5» characterized thereby that the logical element consists of two AND gates having inverted outputs, which are controllable from the same shift registe element for one code word bit on the one hand, and from the shi t registe elemen for the polarit information on the other hand* and the outputs thereof are connected to the electronic switches which connect the sources of voltage and thereby tha the third electronic switch is controllable directly by the information from the shift register element for a code word bit. 7.- Apparatus for the conversion of digital signals with positive and negative values of current or voltage, substantially as desc illustrated in the ac