Apparatus for converting digital values into analog values

Abstract: A first matrix relationship is defined by a plurality of switches operative in first and second states in accordance with the logic levels of binary signals introduced to the switch­ es. The switches in the matrix relationship receive binary signals of relatively high binary significance. An activating line is connected to the matrix relationship to activate storage members, such as capacitors, connected to the matrix re­ lationship. The number of storage members energized by the activating line at each instant is related to the value coded by the logic levels of the binary signals introduced to the matrix relationship. For increasing binary values, the storage mem­ bers previously energized in the plurality by the activating line continue to be energized and additional storage members in the plurality are energized. An interpolating line is also pro­ vided in the first matrix relationship. The interpolating line receives a voltage related to the binary value coded by the logic levels of the binary signals of relatively low binary signi­ ficance. This voltage may be produced by a second matrix relationship of conventional construction. This voltage is in­ troduced through the interpolating line to a particular one of the storage members in the plurality, this storage member constituting the next to be connected to the activating line for increasing binary values. An output signal is produced corres­ ponding to the cumulative value of the energy stored in the storage members in the plurality and in the particular storage member. The output signal may be produced by an integrator amplifier connected to the storage members in the plurality.

Description: This invention relates to apparatus for converting data between a digital form and an analog form. More particularly, the invention relates to apparatus which provides such conversion instantaneously and on a monotonic basis and with minimal differential and integral errors. Various types of equipment receive information in analog form. Such equipment includes process control equipment, measuring instruments, communications equipment and a wide variety of other equipments. Digital computers and data processing systems often receive input parameters in analog form from such equipment and convert these parameters to digital form for processing in the computer or the data processing equipment. After the analog information has been converted to digital information and has been processed, the output information from the digital computer or the data processing equipment is often converted to analog form. By converting the digital information to analog form, the user can assimilate the information in ways which would be difficult if the information remained in digital form. A good example of the conversions discussed in the previous paragraph is in the recording and reproduction of music. The music is produced in analog form. It is converted to digital form by recently developed data processing techniques and is recorded on a medium such as a tape or a disc. When the music is to be reproduced, it is converted again to analog form because this is the form which is necessary to operate sound transducers to give meaning to the listener when he hears the music. As digital computers and data processing equipment have become widespread throughout industry and the office and have even become common in the home, the need for inexpensive, simple and reliable apparatus for converting information between digital and analog forms has become of increasing concern. A considerable effort has been devoted over a period of several decades to provide for converting apparatus which is simple, inexpensive and reliable. In spite of such efforts, the converting apparatus now in use does not meet such criteria. The converting apparatus now in use also has other problems of long standing. For example, the converting apparatus now in use may not be monotonic unless it is quite expensive and complex. By "monotonic" is meant that digital information of progressively increasing value is converted to analog information of progressively increasing value without any decrease in the analog value as the digital value progressively increases. The converting apparatus now in use also has relatively high differential and integral nonlinearities unless the apparatus is quite expensive and complex. Integral nonlinearities result from errors produced in a conversion between digital and analog values over a wide range of such values. Differential nonlinearities result in errors produced in a conversion between digital and analog values over a relatively narrow range of such values. The converting apparatus now in general use also has a problem of major proportions. This results when the converter is operating near the mid-point of its full scale range, or near mid-scale, and digital values are increased incrementally by a single digit. For example, mid-scale problems result in the 12 bit converters now in use when a binary representation of 2047 is converted to a binary representation of 2048. This results from the fact that the binary representation of 2047 is represented by 011111111111 and a binary representation of 2048 is represented by 100000000000 where the least significant digit is at the right. Thus, at mid-scale, the value of every one of the binary digits changes. As all the binary values change, different weighting elements within the converter are selected and discontinuities may occur. These discontinuities may prevent the converter from being truly monotonic. This problem even exists in converters which are made quite complex in an attempt to overcome the problem. From DE-OS 31 29 338 an analog to digital converter is known, comprising a digital to analog converter as a local decoder, an array of capacitances for producing the binary bits with high binary specificance of a digital output signal. The plurality of capacitances each having a binary specificance and a plurality of switches are connected to the input line of an analog signal and reference line. For producing the binary bits with low binary significance, a chain of resistors and a plurality of switches are provided. The array of capacitances is controlled by a successive approximation register, which produces pulses in accordance with the output signal. The pulses connect each of the capacitances selectively with a predetermined potential in order to charge the capacitances with energy. The voltage of the capacitors are compared in a voltage comparator with the ground potential, supplied to a logic circuit and fed back to the array of capacitances. From EP 01 45 335 an apparatus for converting data between digital and analog values is known. A tree of field effect transistor switches comprises pairs of complimentary switches arranged in a succession of levels with the switches at each level controlled by a digital signal on a corresponding input line. Each pair of highest level switches is connected to a corresponding capacitor. All of the capacitors are connected to a charging current source and a periodically operated discharging switch. The switches connect down through the tree levels to main output line, a complimentary output line and an interpolation line. When the capacitors are discharged by closing the switch, the number of capacitors which discharge to the output line represents the digital value on the input lines. One capacitor always discharges to the interpolation line to provide a scaled down charging current for a lower significant converter. The remaining capacitors discharge to the complimentary output line. The present invention provides a digital to analog converter as defined with the features of patent claim 1. Preferred embodiments are subject to the dependent claims. In the invention, a tree-like array relationship is defined by a plurality of switches which are operative in first and second states in accordance with the logic levels of binary signals introduced to the switches. An activating line is coupled to the tree-like array relationship to activate a plurality of storage means which are constructed to receive energy from said activating line. The number of switches in the array relationship is directly related to the binary significance of the binary signals introduced to the switches. For increasing the digital value progressive ones of the storage means in the plurality are energized by the activating line. An interpolating means is provided for introducing a voltage related to the value represented by a plurality of LSB binary signals to a single one of the storage means. An output signal is produced in accordance with the cumulative value of energy stored in the plurality of storage means and the energy stored in the single one of the storage means. The present invention will become even more apparent by the explanation of the preferred embodiments with reference to the accompanied drawings. Figure 1 is a circuit diagram, partially in block form of one embodiment of this invention for converting between digital and analog values; Figure 2 is a circuit diagram which shows in additional detail certain of the features shown in block form in Figure 1; Figure 3 is a circuit diagram which shows in additional detail an output stage shown in block form in Figure 1; and Figure 4 is a truth table illustrating the operation of the circuitry shown in figure 2. Figure 1 illustrates one embodiment of the invention. This embodiment includes two different converters respectively indicated on a general basis at 10 and 12. Each of the converters 10 and 12 may include a plurality of switches connected in a matrix relationship. The converter 10 may be constructed in a number of different embodiments, all conventional. The converter 10 may also be constructed in various embodiments such as disclosed in EP 0 145 335. Each of the converters 10 and 12 converts into analog form digital values preferably coded by the logic levels of binary signals. These binary signals may have first and second logic levels respectively representing a binary "1" and a binary "0". The converter 10 converts the logic levels of binary signals of relatively low binary significance into analog form and the converter 12 converts the logic levels of binary signals of relatively high binary significance into analog form. The converter 10 is shown in Figure 1 as converting three binary bits into analog form, as represented by the magnitude of an output voltage from the converter. These binary bits are the three (3) binary bits of least binary significance. However, as will be appreciated, the converter 10 may convert any desired number of binary bits into analog form. Similarly, the converter 12 is shown in Figure 2 as converting three binary bits into analog form, as represented by the magnitude of an output current from the converter. These are the three (3) binary bits of highest binary significance. It will be appreciated, however, that the converter 12 may convert any desired number of binary bits into analog form. The signals coded to represent the three least significant bits of a digital value coded in binary form are introduced in Figure 1 through lines 14 into a decoder 16 which may be constructed in a conventional manner. The decoder 16 is operatively coupled to a plurality of normally open switches 18, 20, 22, 24, 26, 28, 30 and 32. The switches 18 through 32 (even numbers only) are connected to a voltage dividing network defined by a plurality of impedances such as resistances 34 through 48 (even numbers only). The resistances 34 through 48 (even numbers only) are connected between a first reference potential such as a voltage source 50 and a second reference potential such as a ground 52. The decoder 16 operates to convert into an analog value the binary bits coded by the logic levels of the binary signals on the lines 14. One of the switches 18 through 32 (even numbers only) is then closed by the decoder 16 in accordance with this analog value. For example, the switch 18 is closed for an analog value of "0"; the switch 24 is closed for an analog value of "3"; and the switch 30 is closed for an analog value of "6". Assuming that the voltage from the source 50 provides a first reference potential such as 1.6 volts, ground voltage is introduced through the switch 18 to an output line 56 upon the closure of the switch 18; a voltage of 0.6 volts is introduced to the line 56 upon a closure of the switch 24; and a voltage of 1.2 volts is introduced to the line 56 upon a closure of the switch 30. The output line 56 from the converter 10 is connected to one contact of a double-pole switch 62. A pole 62B of the switch 62 is connected to an interpolation line 58 in the converter 12 and that pole may be connected to either the output line 56 or to a second contact which is connected to the second reference potential such as the ground 52. The converter 12 also includes an activation line 60 which is connected to the other pole 62A of the double-pole switch 62. One contact of the pole 62A is connected to the second reference potential such as the ground 52 and the other contact of the pole 62A is connected to the source of the first reference potential. An energy storage discharge line 64 of the converter 12 preferably receives the second reference potential such as the ground 52. The converter 12 includes a matrix, generally indicated at 65, which is formed from a plurality of switches. The matrix 65 is shown in detail in Figure 2. Output terminals from the matrix 65 are connected to energy storage members such as capacitors 66 through 80 (even numbers only). Only some of these capacitors are shown in Figure 1 but all are shown in Figure 2. The charges in selected ones of the capacitors 66 through 80 (even numbers only) are introduced to a line 82 in Figure 1. The matrix 65 is constructed to connect successive ones of the capacitances 66 through 80 (even numbers only) to the activating line 60 for progressively increasing values coded by the logic levels of the binary signals introduced to the matrix 65 through lines 84 in Figure 1. The capacitances connected to the line 60 become charged by the voltage produced on such line when the line is connected by the pole 62A to the source 50 of the first reference potential. As a result, the output current passing from the voltage source 50 through the matrix 65 and the capacitances to the line 82 has a magnitude corresponding to the value of the most significant bits coded by the logic levels of the binary signals in the lines 84. For every value represented by the binary signals in the lines 84, a particular one of the capacitances 66 through 80 is connected to the interpolation line 58. This particular capacitance is the one next to be connected to the line 60 for increasing values coded by the logic levels of the binary signals in the lines 84. This particular capacitance then becomes charged when the pole 62B connects the capacitance to the voltage on the line 56 and this charge is introduced to the output line 82. As a result, the output line 82 provides at each instant a voltage which has a magnitude corresponding to the analog value coded by the logic levels of the binary signals in the lines 14 and 84. The switch 62 is periodically operative to position the two poles of the switch against the botton contacts of the switch in Figure 1 and then against the top contacts of the switch in Figure 1. When the two poles of the switch 62 engage the bottom contacts of the switch, all of the capacitances 66 through 80 (even numbers only) discharge through the switch to the second reference potential such as the ground 52. An amplifier 200 is then reset by activating the reset signal on a reset line 210 and the output line 206 of the digital-to-analog converter is forced to a voltage near the second reference potential 52. The reset signal is then de-activated and the poles of switch 62 then engage the top contacts of the switch in Figure 1. The particular capacitances 66 through 80 selected by the binary signals on lines 84 (even numbers only) are connected to the activating line 60 and become changed by the voltage from the first reference source 50 and the particular interpolation capacitance becomes charged in accordance with the voltage on the line 56. The line 82 then produces a voltage having a magnitude corresponding to the analog value coded by the logic levels of the binary signals on the lines 14 and 84. A preferred embodiment of the matrix 65 is shown in Figure 2. The matrix 65 includes the interpolation line 58, the activation line 60 and the discharge line 64. The matrix 65 also includes a plurality of double pole switches 100 through 126 (even numbers only). The switches 100 and 102 may be considered to constitute a first sub-set; the switches 104, 106, 108 and 110 may be considered to constitute a second sub-set; and the switches 112 through 126 may be considered to constitute a third sub-set. Each sub-set of switches receives, from an individual one of the lines 84, logic levels of binary signals having an individual binary significance. The switches 100 and 102 receive logic levels of binary signals having a lower binary significance than the binary signals received by the switches in the other sub-sets and the switches 104, 106, 108 and 110 receive logic levels of binary signals having a lower binary significance than the logic levels of the binary signals received by the switches 112 through 126 (even numbers only). As will be seen, the number of switches in each of the sub-sets is directly proportional to the binary significance of the binary signals introduced to that sub-set. The switches shown in Figure 2 are mechanical. However, as will be appreciated, the switches may be solid state. When solid state switches are employed, each of the switches 100 through 126 (even numbers only) may be replaced by a pair of switches. Actually, each of the switches 100 through 126 (even numbers only) may be considered as a pair with the movable contact and one pole defining one switch in the pair and the movable contact and the other pole defining the other switch in the pair. One contact of the switch 100 is common with the line 64 and the other contact in the switch 100 is common with the line 58. Similarly, one contact in the switch 102 is common with the line 60 and the other contact in the switch is common with the line 58. Connections are made from the movable poles of the switch 100 to first contacts of the switches 104 and 106. Similarly, connections are made from the movable poles of the switch 102 to first contacts of the switches 108 and 110. The second contact of the switch 104 is connected to the line 64 and the second contact of the switch 106 is connected to the line 60. Connections are correspondingly made from the second contact of the switch 108 to the line 64 and from the second contact of the switch 110 to the line 60. The movable poles of the switches 104, 106, 108 and 110 are respectively connected to first contacts of the switches 112 and 114, first contacts of the switches 116 and 118, first contacts of the switches 120 and 122 and first contacts of the switches 124 and 126. The second contact of the switches 112, 116, 120 and 124 are connected to the line 64 and the second contacts of the switches 114, 118, 122 and 126 are connected to the line 60. The movable poles of the switches 112 through 126 (even numbers only) are respectively connected to first terminals of the capacitors 66 through 80 (even numbers only). As will be seen in Figure 2 and as will be also seen in Figure 4, the capacitors 66 through 80 (even numbers only) are respectively designated by the numerals H through A. The movable poles of the switches 100 through 126 (even numbers only) are shown in Figure 2 in the positions in which they are operative when the binary signals introduced to the switches have a logic level of "0". When the logic levels of the binary signals introduced through the lines 84 to the switches 112 through 126 (even numbers only) are coded to represent a binary "1", the movable poles of the switches move from engagement with the lower contacts in Figure 2 to engagement with the upper contacts in that Figure. With the movable contacts of the switches 100 through 126 (even numbers only) in the positions shown in Figure 2, no connections are established between any of the capacitors 66 through 80 (even numbers only) and the activating line 60. As a result, none of the capacitors 66 through 80 (even numbers only) is charged by the voltage on the line 60. This corresponds to a binary value of "0" in accordance with the logic levels of the binary signals introduced to the lines 84. However, a connection is established which includes the interpolation line 58, the switch 102, the switch 110, the switch 126 and the capacitance 80. Then, when the poles of the switch 62 in Figure 1 are moved to the upper contacts, this causes the capacitance 80 to become charged to a level dependent upon the voltage on the interpolating line 58, this voltage being received from the second matrix output line 56 through the pole 62B. As a result, a signal is introduced to the line 82 in Figure 1 in accordance with the analog value coded by the logic levels of the binary signals introduced through the lines 14 (Figure 1) to the converter 10. When the analog value coded by the logic levels of the binary signals introduced to the lines 84 in Figure 1 has a value of "1" or binary "001" (the least significant binary bit being at the right), this causes the movable arms of the switches 100 and 102 to be moved in Figure 2 to a position engaging the upper contacts of the switches. A connection is accordingly established which includes the activating line 60, the switch 102, the switch 110, the switch 126 and the capacitance 80. When the poles of switch 62 in Figure 1 are moved to the upper contacts, this causes the capacitance 80 to be charged to a value equal to the first reference voltage on the line 50 in Figure 1. At the same time, a connection is established which includes the interpolating line 58, the switch 100, the switch 106, the switch 118 and the capacitance 72. The capacitance 72 accordingly becomes charged to a value dependent upon the voltage on the interpolating line 58. Since the charges in the capacitances 80 and 72 are introduced to the line 82 in Figure 1, the total charge delivered to the line 82, and hence the voltage on the integrating amplifier output line 206 in Figure 1, represents the analog value coded by the logic levels of the binary signals in the lines 14 and 84 in Figure 1. Similarly, for an analog value of "2", or binary "010" coded by a logic level of binary "1" on the line S1 in Figure 1, the capacitances 80 and 72 become charged through a circuit including the first reference voltage source 50 and the activation line 60 when the switch 62A is operated to energize the activation line 60. At the same time, the capacitor 76 becomes connected to the line 58 so as to become charged to a level dependent upon the voltage received through the pole 62B from the output line 56. Figure 4 indicates the capacitances which are respectively connected to the lines 60 and 58 for each analog value coded by the logic levels of the binary signals on the lines 84. As will be seen in Figure 4, the logic levels of the binary signals introduced to the lines 84 are indicated in the first three columns in Figure 4. The analog significance of these binary signals is shown at the top of each of these columns. The remaining columns (with the exception of the last column) indicate the state of operation of the capacitances 66 through 80 (even numbers only), these capacitances being respectively indicated in Figure 4 by the letters "H" through "A" to correspond to the letters indicated for these capacitances in Figure 2. The last column in Figure 4 indicates the particular one of the capacitances to be connected to the interpolation line 58 for each analog value coded by the logic levels of the binary signals on the lines 84. As will be seen in Figure 4, two diagonal lines 130 and 132 are provided. The capacitances indicated to the left of the line 130 represent those connected to the activation line 60 for the different analog values. The capacitances isolated between the lines 130 and 132 are those which are connected to the interpolation line 58 for each analog value. These capacitances correspond to those indicated in the last column in Figure 4. As will be seen, the capacitance connected to the interpolation line 58 for each analog value is the one next to be connected to the activation line 60 when the analog value represented by the logic levels of the binary signals coded on the lines 84 increases. The signal on the line 82 in Figure 1 is applied to a stage, generally indicated at 200, for producing an output voltage representative at the end of each conversion cycle of the energy delivered to the line 82 by the energy storage means. The stage 200 is shown as a single block in Figure 1 and is shown in additional detail in Figure 3. The stage 200 may include an integratoring amplifier and a circuit for resetting the voltage produced at the output of the integrating amplifier in response to a reset signal on a line 210. The integrating amplifier may include a high-gain operational amplifier 202 in Figure 3. One input terminal of the amplifier 202 receives the voltage on the line 82 and another input terminal of the amplifier has a common connection with the second reference potential such as the ground 52. A capacitance 204 in Figure 1 is connected between the input terminal 82 and an output terminal 206 of the amplifier 202. A resistance 207 and a reset switch 208 are in series across the capacitance 204. The reset switch closes in response to a reset signal on the line 210. The signal charge on the line 82 is introduced to the operational amplifier 202, which operates in conjunction with the capacitance 204 to integrate this signal charge. As a result, during the opened state of the switch 208, the capacitance 204 receives the signal charge. This signal charge corresponds to the analog value coded by the logic levels of the binary signals on the lines 14 and 84 in Figure 1. When the switch 208 becomes closed, the charge in the capacitance 204 is discharged through the switch 208 and the resistance 207 and the voltage at the output line 206 is reset to a value that differs from the second reference potential such as ground only by the small input offset voltage and any noise in the operational amplifier 202. The operation of the switch 208 is synchronized with the operation of the switch 62 so that the switch 208 is open during the period of connection of the movable pole of the switch 62 to the upper contacts in Figure 1 and is closed during the period of connection of the movable pole of the switch 62 to the lower contacts of the switch 62 in Figure 1. In this way, the capacitance 204 becomes charged during the same period as the charging of the selected ones of the capacitances 66 through 80 (even numbers only) and the capacitance 204 becomes discharged at the same time that the capacitances 66 through 80 (even numbers only) become discharged. As a result, a square wave pulse is produced on the line 206 with a magnitude indicating the analog value coded by the logic levels of the binary signals on the lines 14 and 84. The apparatus disclosed above has certain important advantages. One of these results from the fact that the capacitance connected to the interpolation line 58 at each instant is the same one to be connected next to the activating line 60 for increasing values coded by the logic levels of the binary signals in the lines 14 and 84. Because of this, the charge delivered to the line 82 corresponding to an increase in the input digital code by a least significant bit from the full output of the second matrix relationship 65 is determined by one and the same capacitor plus the same stray capacitance of that capacitor. This minimizes any error which is produced in the charge signal on the line 82 in Figure 1. These advantages enhance the monotonicity of the converter constituting this invention and help to minimize any integral and differential linearity errors in the converter. Another important advantage in applicant's invention is that each of the capacitances 66 through 80 (even numbers only) in the converter 12 has substantially the same layout on an integrated circuit chip and consequently the same value. This is particularly significant in view of the fact that the capacitance connected to the interpolation line 58 for each analog value also has the same value. Furthermore, the capacitances 66 through 80 (even numbers only) are individually connected to the activation line 82 for progressively increasing values. As the values progressively increase, the capacitances previously connected to the line 82 remain connected to the line and additional capacitances are connected to the line. All of the features discussed in this paragraph insure that the signal on the line 82 is monotonic and that minimal transients are produced then the magnitude of the signal on the line 82 changes. In view of the advantages discussed in the previous paragraphs, a conventional amplifier such as the integrating amplifier 200 can be used to convert to an analog voltage the charge signals from the matrix relationship 10 and the matrix relationship 12. Furthermore, the deviations allowable in the accuracy of the components of the matrix relationship 10 such as the resistance ladder formed by the resistances 34 through 48 (even numbers only) can be less stringent than in corresponding apparatus of the prior art. For example, when the apparatus constituting this invention operates upon sixteen (16) binary bits, the converter 12 may operate upon a number of bits such as the ten (10) most significant binary bits and the converter 10 may operate upon the remaining number of bits such as the six (6) least significant binary bits. Under such circumstances, the resistances 34 through 48 (even numbers only) may have deviations in value as high as two percent (2%) while still maintaining monotonicity of the apparatus of this invention. When deviations in value as high as two percent (2%) are allowable in components such as resistors, the resistors can be manufactured using low cost monolithic techniques while still retaining monotonicity and low integral and differential errors in the apparatus constituting this invention. It is also relatively easy to provide resistors within such limits of deviations because the resistances 24 through 38 (even numbers only) may be considered to constitute a single resistor with a number of taps. The apparatus constituting this invention also has other important advantages. For example, because the converter 12 may have to convert only the ten (10) most significant bits out of a total of sixteen (16) bits to be converted, the apparatus constituting this invention can be disposed on a single integrated circuit chip. The conversion of a minimal number of bits in the converter 12 is desirable because the number of switches in the converter approximately doubles for each additional binary bit which is to be decoded by the converter. The ability to provide sixteen (16) bits on a single integrated chip is particularly important when the apparatus constituting this invention is used to convert logic levels of binary signals into audible sound. One reason is that the digital audio reproducers now in use reproduce into audible sound the logic levels of binary signals coding sixteen (16) binary bits recorded on a compact disc to code for analog information. This recording ability is particularly important when, as in applicant's invention, the converting apparatus is able to convert the signals coding the sixteen (16) binary bits into analog information on a monotonic basis and with minimal and differential errors. As will be appreciated, the output on the line 82 is a charge. It is desirable to provide an output in the form of a charge rather than in the form of a current because it is easier to provide a precision charge output, particularly on an integrated circuit chip with components formed in C-Mos technology, rather than a precision current output. There are also other important advantages to applicant's invention. This results from the use by applicant of an integrating-amplifier, such as that formed by the amplifier 202 and the capacitor 204, to convert the signal on the line 82 to an output voltage on the line 206 in Figure 3. An integrating-amplifier is relatively accurate and relatively easy to build in comparison to other types of output stages. The apparatus of this invention can be used in a wide variety of fields. As previously discussed, the apparatus of this invention is particularly adapted to be used to convert into audible sound of considerable fidelity the logic levels of binary signals recorded on a compact disc and coded in binary form to represent such analog information. However, even when capacitances such as the capacitances 66 through 80 (even numbers only) are used to produce the analog conversion, the apparatus constituting this invention has the capability of being operated at much higher rates than would be normally expected. This results in part from the advantages inherent in applicant's invention and described in some detail above. As a result, applicant's invention can advantageously be used in a number of other fields including telecommunications, process controls and robotics. Although this invention has been disclosed and illustrated with reference to particular embodiments, the principles involved are susceptible of use in numerous other embodiments which will be apparent to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the appended claims.

Claims: Digital to analog converter comprising means (84) for providing a plurality of binary signals of high binary significance each having first and second logic levels respectively representing a binary "1" and a binary "0", the binary signals in the plurality cumulatively coding the digital value in binary form, each of the binary signals in the plurality having the same logic levels as the other binary signals, each of the binary signals in the plurality having an individual binary significance, a plurality of switches (100-126) connected in a tree-like array relationship, each of the switches (100-126) in the plurality having first and second states of operation, the switches (100-126) in the plurality being disposed in sub-sets each responsive to an individual one of the binary signals of high binary significance to provide for an operation of the switches (100-126) in the first and second states in accordance with the logic levels of each individual one of the binary signals, the number of switches in each subset being directly related to the binary significance of the binary signals of high binary significance introduced to such subset, a plurality of storage means (66-80) each having the same capacitance value as the other storage members and constructed to receive and store energy from an activating line (60), said activating line (60) being coupled to the switches (100-126) in the subsets at the input ends of the switches, the storage means (66-80) in the plurality being coupled to the output ends of the switches (100,126) in the tree-like array relationship, for producing charges in the storage means in accordance with the operation of the switches, the tree-like array relationship providing for the introduction of energy to progressive ones of the storage means (66-80) in the plurality for progressive increases in the digital value, means (10,16) for obtaining a voltage related to the value coded by the logic levels of LSB binary signals, said LSB binary signals having a binary significance lower than that of the switches of lowest binary significance in the tree-like array relationship, means (200,206) for producing an output voltage in accordance with the charges in the storage means, interpolating means (58) for introducing, via the switches (100-126) in the tree-like array relationship, to a single one of the storage means (66-80) in the plurality, the voltage related to the value represented by the plurality of said LSB binary signals. Digital to analog converter according to claim 1, wherein the single one of the storage means (66-80) receiving the voltage related to the value representing the LSB binary signals is the next to be connected in the tree-like array relationship to receive energy for increasing binary values in accordance with the value coded by the logic levels of the binary signals of high binary significance. Digital to analog converter according to claim 1 or 2 wherein the switches in the sub-sets are connected in the array relationship to introduce energy from the activating line (60) to progressive numbers of storage means (66-80) in the plurality for increasing binary values coded by the logic level of the binary signals introduced to the sub-sets and to retain the same storage means (66-80) for the introduction of energy, for such increasing binary values, as have received energy from the activating line (60) for reduced values coded by the logic leavels of such binary signals. Digital to analog converter according to at least one of claims 1 to 3 comprising: means (10) defining a second one-dimensional array relationship, means (16) for introducing the LSB binary signals to the second array relationship to obtain from the second array relationship a voltage related to the value coded by the logic levels of the LSB binary signals. Digital to analog converter according to at least one of claims 1 to 4 comprising means (64) for discharging the energy in the storage means (66-80) after the output signal has been produced. Digital to analog converter according to at least one of claims 1 to 5 comprising means (62A) for applying a reference voltage to the storage means (66-80) connected to the tree-like array relationship for the storage of energy in accordance with the binary signals of high binary significance after such storage means (66-80) have been connected to the first array relationship. Digital to analog converter according to at least one of claims 1 to 6 wherein: the means (10, 16) responsive to the LSB binary signals produce a first voltage having a magnitude related to the binary value coded by such binary signals, the plurality of switches (100-126) in the tree-like array relationship are connected to the storage means (66-80) in the plurality and to a first line (56) for coupling first particular ones of the storage means in the plurality to the first line in accordance with the value coded by the binary signals of high binary significance, and further comprising means for introducing the first voltage to a second particular one of the storage means in the plurality, the second particular one of the storage means in the plurality being next included in the first particular ones of the storage means in the plurality for increasing binary values coded by the logic levels of the binary signals in the plurality, means for introducing energy to the first particular ones of the storage means in the plurality, and means responsive to the energy stored in the first particular ones of the storage means in the plurality and in the second particular one of the storage means in the plurality for providing an output indication of such stored energy. Digital to analog converter according to at least one of claims 1 to 7 comprising: means (62) connecting the interpolation line (58), the activating line (60), the switches in the plurality and the storage means (66-80) in the plurality to provide for a connection to the activating line (60) of a number of the storage means (66-80) in the plurality related to the value coded by the logic levels of the binary signals of high binary significance and to provide for the connection to the interpolation line (58) of the single one of the storage means in the plurality other than the storage means connected to the activating line, means for providing for the activation of the storage means (66-80) connected in the plurality to the activating line (60), and means for providing an output indication of the energy stored in the storage means connected to the activating line (60) and the interpolation line (58). Digital to analog converter according to claim 8 wherein the connecting means (62) connects to the interpolating line (58) the next of the storage means to be connected in the plurality to the activating line (60) for increasing binary values coded by the logic levels of the binary signals in the plurality. Digital to analog converter according to at least one of claims 7 to 9 wherein the switches connected in the tree-like array relationship and responsive to the binary signals of high binary significance in the plurality produce a flow of current having a magnitude related to the binary value of the binary signals of high binary significance and to the first voltage, and further comprising means responsive to the flow of current in the array relationship for producing an output voltage having a magnitude related to the magnitude of such current flow. Digital to analog converter according to claim 10 wherein the switches in the tree-like array relationship are being constructed to produce a flow of current through a number of the storage means (66-80) in the plurality in accordance with the value coded by the logic levels of the binary signals of high binary significance and to produce a flow of current through the single one of the storage means in the plurality in accordance with the magnitude of the first voltage. Digital to analog converter according to one of claims 1 to 11 wherein the array relationship defined by the switches in the plurality is constructed to isolate the single one of the storage means for each binary value coded by the logic levels of the LSB binary signals and wherein the single storage member is the next to receive energy in accordance with the value coded by the logic levels of the binary signals of high binary significance when the value coded by the logic levels of the binary signals in the plurality is increasing. Digital to analog converter according to at least one of claims 1 to 12 wherein the storage means constitutes capacitors (66-80) and the output signal producing means (200) constitutes an integrating amplifier (202). Digital to analog converter according to claim 13 wherein the output signal producing means (200) includes a capacitor (204) for receiving a charge representative of the analog value of the output signal and means (207, 208) which are associated with the capacitor (204) in the integrating amplifier (202) for discharging the capacitor (204) after the storage in the capacitor (204) of the charge representative of the analog value.

Inventors: LEWYN LANNY L, LEWYN, LANNY L.
Applicants: BROOKTREE CORP, BROOKTREE CORPORATION
Application year: 1986
Main classification: H03M1
IPC codes: H03M1