Abstract:
A digital-to-analog converter (DAC) circuit includes a least significant bit (LSB) set of capacitors, each commonly coupled to an LSB node, and a most significant bit (MSB) set of capacitors, each coupled to an MSB node. A section-coupling capacitor couples the LSB and MSB nodes. The LSB node exhibits a parasitic capacitance, which tends to introduce a jump error voltage. Digital input signals are applied to the LSB and MSB capacitors, and in response, an analog output signal is developed on the MSB node. A compensation capacitor coupled to the MSB node has a compensation capacitance selected to offset the jump error voltage introduced by the parasitic capacitance. The compensation capacitor is enabled when all of the LSB capacitors are coupled to digital input signals having a logic ‘0’ state. Otherwise, the compensation capacitor is disabled (e.g., left in a floating state).

Description:
FIELD OF THE INVENTION 
     The present invention relates to analog-to-digital conversion (ADC) and/or digital-to-analog conversion (DAC) systems. 
     RELATED ART 
       FIG. 1  is a circuit diagram of a conventional successive approximation register (SAR) ADC/DAC circuit  100 , which includes a two-section capacitor array. SAR ADC/DAC circuit  100  includes comparator  101 , successive approximation registers (SARs)  102   X  and  102   Y , least significant bit (LSB) capacitor section  103 , most significant bit (MSB) capacitor section  104 , section coupling capacitors C SX  and C SY , LSB switches S LX0 -S LX(K-1)  and S LY0 -S LY(K-1) , MSB switches S MX0 -S MX(M-1)  and S MY0 -S MY(M-1) , and common mode switches S X  and S Y . LSB capacitor section  103  includes LSB capacitors C LX0 -C LX(K-1)  and C LY0 -C LY(K-1) . MSB capacitor section  104  includes MSB capacitors C MX0 -C MX(M-1)  and C MY0 -C MY(M-1 ). Each of the LSB capacitors C LX(n) , C LY(n)  and each of the MSB capacitors C MX(n) , C MY(n)  has a capacitance equal to 2 n *C, wherein C is a unit capacitance. Each of the section coupling capacitors C SX  and C SY  has a capacitance equal to the unit capacitance, C. 
     Parasitic capacitors/capacitances C PA  and C PB  exist on the output nodes A and B, respectively, of LSB capacitor section  103 . Each of these parasitic capacitances C PA  and C PB  has a value of C P *C. Each of the parasitic capacitances C PA  and C PB  is error source that introduces a non-linear characteristic to SAR ADC/DAC circuit  100 . The parasitic capacitances C PA  and C PB  cannot be avoided in the LSB output nodes A and B, respectively. 
     The combined capacitance of LSB capacitors C LX0 -C LX(K-1) , section coupling capacitor C SX  and the parasitic capacitor C PA  can be represented by the following equation.
 
 C   LSB   =C *(2 k −1+ C   P )/(2 k   +C   P )  Eq. (1)
 
     The total capacitance at the output node X can be represented by the following equations.
 
 C   TOT   =C   LSB +(2 m −1)* C   Eq. (2)
 
 C   TOT   =C *(2 (k+m) +2 m   *C   P −1)/(2 k   +C   P )  Eq. (3)
 
     In general, SAR ADC/DAC circuit  100  operates as follows. During a sample mode, switches S X  and S Y  are closed, thereby applying a common mode voltage VCM to nodes X and Y, respectively. Switches S LX0 -S LX(K-1)  and S MX0 -S MX(M-1)  are controlled to route input voltage VIN+ to capacitors C LX0 -C LX(K-1)  and C MX0 -C MX(M-1) . Similarly, switches S LY0 -S LY(K-1)  and S MY0 -S MY(M-1)  are controlled to route input voltage VIN− to capacitors C LY0 -C LY(K-1)  and C MY0 -C MY(M-1) . As a result, capacitor sections  103  and  104  sample the differential input signal represented by signals VIN+ and VIN−. 
     Comparator  101  provides analog output voltages Q# and Q in response to the sampled differential input voltages VIN+ and VIN−, respectively. SARs  102   X  and  102   Y  receive these analog output voltages Q# and Q, and in response, provide digital output signals. The digital output signals provided by SAR  102   X  are loaded into switches S LX0 -S LX(K-1)  and S MX0 -S MX(M-1) . Similarly, the digital output signals provided by SAR  102   Y  are loaded into switches S LY0 -S LY(K-1)  and S MY0 -S MY(M-1) . The loaded digital signals cause the switches S LX0 -S LX(K-1) , S LY0 -S LY(K-1) , S MY0 -S MY(M-1)  and S MX0 -S MX(M-1)  to selectively route a positive reference voltage VRP or a negative (or ground) reference voltage VRN to the associated capacitors. As described herein, the application of the reference voltage VRP to a capacitor represents a logic ‘1’ state, and the application of the reference voltage VRN to a capacitor represents a logic ‘0’ state. The SARs  102   X  and  102   Y  iteratively modify the digital output signals in response to the analog output signals Q# and Q, until the digital output signals accurately approximate the differential input signals VIN+ and VIN−. The exact manner of operating SAR ADC/DAC circuit  100  is known to those of ordinary skill in the art. 
       FIG. 2  is a graph  200 , which illustrates the manner in which the output voltage V X  varies in response to changes in the digital signals provided by SAR  102   X . In the illustrated example, k=3 and m=4, such that there are three LSB capacitors (C LX0 -C LX2 ) and four MSB capacitors (C MX0 -C MX3 ). The SAR code is illustrated as a seven bit value, which can be generally represented as ‘ABCD EFG’, wherein ‘ABCD’ represent the states of MSB capacitors C MX3 -C MX0 , respectively, and ‘EFG’ represent the states of LSB capacitors C LX2 -C LX0 , respectively. A logic ‘0’ value indicates that the associated capacitor is coupled to receive the negative/ground reference voltage VRN, and a logic ‘1’ value indicates that the associated capacitor is coupled to receive the positive reference voltage VRP. As illustrated in  FIG. 2 , a jump voltage, V JUMP , exists when the SAR code is incremented from a value of ‘xxx0 111’ to a value of ‘xxx1 000’. This jump voltage V JUMP  is significantly greater than the voltage, LSB, which exists during other transitions of the SAR code. This jump voltage V JUMP  thereby represents a non-linear response in the output voltage V X . 
     The jump voltage V JUMP  can be determined as follows. The voltage V X  can be represented by the following equations, when all of the LSB capacitors C LX0 -C LX(K-1)  are coupled to the positive reference voltage VRP, and all of the MSB capacitors C MX0 -C MX(M-1)  are coupled to the negative/ground reference voltage VRN.
 
 V   LSB   =C   LSB   /C   TOT   *Vr *(2 k −1)/(2 k −1+ C   P )  Eq. (4)
 
 V   LSB   =Vr *(2 k −1)/(2 k+m −1+2 m   *C   P )  Eq. (5)
 
     The voltage V X  can be represented by the following equations, when all of the LSB capacitors C LX0 -C LX(K-1)  are coupled to the negative/ground reference voltage VRN, the MSB capacitor C MX0  is coupled to the positive reference voltage VRP, and the remaining MSB capacitors C MX1 -C MX(M-1)  are coupled to the negative/ground reference voltage VRN.
 
 V   MSB   =C/C   TOT   *Vr   Eq. (6)
 
 V   MSB   =Vr *(2 k   +C   P )/(2 k+m −1+2 m   *C   P )  Eq. (7)
 
     The jump voltage V JUMP  can be represented by the following equations.
 
 V   JUMP   =V   MSB   −V   LSB   Eq. (8)
 
 V   JUMP   =Vr *(1 +C   P )/(2 k+m −1+2 m   *C   P )  Eq. (9)
 
     Equation (5) represents the voltage V X  associated with 2 K −1 unit capacitances C. The voltage V X  associated with a single unit capacitance C can therefore be represented by the following equations.
 
 LSB=V   LSB /(2 K −1)  Eq. (10)
 
 LSB=Vr /(2 k+m −1+2 m   *C   P )  Eq. (11)
 
     The difference between the jump voltage V JUMP  and the voltage V X  associated with a single unit capacitance represents (LSB) the jump error voltage, which is defined by the following equations.
 
Δ V   e   =V   JUMP   −LSB   Eq. (12)
 
Δ V   e   =Vr*C   P /(2 k+m −1+2 m   *C   P )  Eq. (13)
 
Δ V   e   =C   P   *LSB   Eq. (14)
 
     It would therefore be desirable to have a SAR ADC/DAC circuit that does not exhibit the jump error voltage ΔVe as defined by equation (14). 
     SUMMARY 
     Accordingly, the present invention provides a SAR ADC/DAC circuit that includes a compensation capacitor that compensates for the jump error voltage ΔVe introduced by the parasitic capacitance C P . 
     In one embodiment, a digital-to-analog converter (DAC) circuit includes a least significant bit (LSB) set of capacitors, each commonly coupled to an LSB node, and a most significant bit (MSB) set of capacitors, each coupled to an MSB node. A section-coupling capacitor couples the LSB and MSB nodes. The LSB node exhibits a parasitic capacitance, which tends to introduce a jump error voltage. Digital input signals are applied to the LSB and MSB capacitors, and in response, an analog output signal is developed on the MSB node. A compensation capacitor coupled to the MSB node has a compensation capacitance selected to offset the jump error voltage introduced by the parasitic capacitance. The compensation capacitor is enabled (e.g., coupled to a ground supply voltage terminal) when all of the LSB capacitors are coupled to digital input signals having a logic ‘0’ state. Otherwise, the compensation capacitor is disabled (e.g., left in a floating state). As a result, the compensation capacitor advantageously offsets the parasitic capacitance when all of the LSB capacitors transition to a logic ‘0’ state. 
     The present invention will be more fully understood in view of the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a conventional SAR ADC/DAC circuit. 
         FIG. 2  is a graph, which illustrates the manner in which an output voltage V X  varies in response to changes in a SAR code in the SAR ADC/DAC circuit of  FIG. 1 . 
         FIG. 3  is a block diagram of a differential SAR ADC/DAC circuit that includes compensation capacitors in accordance with one embodiment of the present invention. 
         FIG. 4  is a block diagram of a differential SAR ADC/DAC circuit that includes series-connected compensation capacitors in accordance with another embodiment of the present invention. 
         FIG. 5  is a block diagram of a single-ended SAR ADC/DAC circuit that includes compensation capacitors in accordance with another embodiment of the present invention. 
         FIG. 6  is a block diagram of a single-ended SAR ADC/DAC circuit that includes series-connected compensation capacitors in accordance with another embodiment of the present invention. 
         FIG. 7  is a block diagram of a differential charge scaling DAC that includes compensation capacitors in accordance with one embodiment of the present invention. 
         FIG. 8  is a block diagram of a differential charge scaling DAC that includes series-connected compensation capacitors in accordance with one embodiment of the present invention. 
         FIG. 9  is a block diagram of a single-ended charge scaling DAC that includes compensation capacitors in accordance with one embodiment of the present invention. 
         FIG. 10  is a block diagram of a single-ended charge scaling DAC that includes series-connected compensation capacitors in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 3  is a block diagram of an SAR ADC/DAC circuit  300  in accordance with one embodiment of the present invention. Because SAR ADC/DAC circuit  300  is similar to SAR ADC/DAC circuit  100 , similar items in  FIGS. 3 and 1  are labeled with similar reference numbers. Thus, SAR ADC/DAC circuit  300  includes comparator  101 , SARs  102   X  and  102   Y , LSB capacitor section  103  (including LSB capacitors C LX0 -C LX(K-1)  and C LY0 -C LY(K-1) ), MSB capacitor section  104  (including MSB capacitors C MX0 -C MX(M-1)  and C MY0 -C MY(M-1) ), section coupling capacitors C SX  and C SY , LSB switches S LX0 -S LX(K-1)  and S LY0 -S LY(K-1) , MSB switches S MX0 -S MX(M-1)  and S MY0 -S MY(M-1) , common mode switches S X  and S Y , LSB output nodes A and B, and MSB output nodes X and Y, which have been described above in connection with  FIG. 1 . 
     In addition to the above-described elements, SAR ADC/DAC circuit  300  includes compensation capacitors C CX  and C CY , compensation capacitor switches S CX  and S CY , and logic control blocks  301  and  302 . Note that parasitic capacitors/capacitances C PA  and C PB  still exist on the output nodes A and B, respectively, of LSB capacitor section  103 . 
     Compensation capacitor C CX  is coupled between MSB output node X and compensation capacitor switch S CX . Similarly, compensation capacitor C CY  is coupled between MSB output node Y and compensation capacitor switch S CY . Compensation capacitor switches S CX  and S CY  are controlled by logic control blocks  301  and  302 , respectively. As described in more detail below, logic control block  301  causes compensation capacitor switch S CX  to selectively couple the associated terminal of compensation capacitor C CX  to the input terminal VIN+, to the negative/ground reference voltage VRN, or leave this terminal of capacitor C CX  floating, in response to the output of SAR  102   X . Similarly, logic control block  302  causes compensation capacitor switch S CY  to selectively couple the associated terminal of compensation capacitor C CY  to the input terminal VIN−, to the positive reference voltage VRP, or leave this terminal of compensation capacitor C CY  floating, in response to the output of SAR  102   Y . 
     In general, SAR ADC/DAC circuit  300  operates in a manner similar to SAR ADC/DAC circuit  100 , with differences noted below. During a sample mode, switches S X  and S Y  are closed, thereby applying a common mode voltage VCM to nodes X and Y, respectively. Switches S LX0 -S LX(K-1) , S MX0 -S MX(M-1)  and S CX  are controlled to route input voltage VIN+ to capacitors C LX0 -C LX(K-1) , C MX0 -C MX(M-1)  and C CX  Similarly, switches S LY0 -S LY(K-1) , S MY0 -S MY(M-1)  and C CY  are controlled to route input voltage VIN− to capacitors C LY0 -C LY(K-1) , C MY0 -C MY(M-1)  and C CY . As a result, capacitor sections  103  and  104 , and compensation capacitors C CX  and C CY , sample the differential input signal represented by signals VIN+ and VIN−. 
     Logic control blocks  301  and  302  are coupled to receive the LSB portion of the digital signals provided by SARs  102   X  and  102   Y , respectively. More specifically, logic control block  301  is coupled to receive the digital signals provided by SAR  102   X , which control LSB switches S LX0 -S LX(K-1) . Similarly, logic control block  302  is coupled to receive the digital signals provided by SAR  102   Y , which control LSB switches S LY0 -S LY(K-1) . After the above-described sample mode is complete (i.e., during a hold/compare mode), if logic control block  301  determines that LSB switches S LX0 -S LX(K-1)  all receive digital signals representative of logic ‘0’ values, then logic control block  301  causes compensation capacitor switch S CX  to couple the associated terminal of compensation capacitor C CX  to the negative/ground voltage VRN. However, if logic control block  301  determines that one or more of LSB switches S LX0 -S LX(K-1)  receive digital signals representative of a logic ‘1’ value, then logic control block  301  causes compensation capacitor switch S CX  to leave the associated terminal of compensation capacitor C CX  in a floating state, effectively de-coupling the compensation capacitance from output node X. 
     Logic control block  302  controls compensation capacitor switch S CY  in a manner similar to the manner in which logic control block  301  controls compensation capacitor switch S CX . More specifically, when logic control block  302  determines that LSB switches S LY0 -S LY(K-1)  all receive digital signals representative of logic ‘1’ values, then logic control block  302  causes compensation capacitor switch S CY  to couple the associated terminal of compensation capacitor C CY  to the positive reference voltage VRP. However, if logic control block  302  determines that one or more of LSB switches S LY0 -S LY(K-1)  receive digital signals representative of a logic ‘0’, then logic control block  302  causes compensation capacitor switch S CY  to leave the associated terminal of compensation capacitor C CY  in a floating state, effectively de-coupling the compensation capacitance from output node Y. 
     The jump voltage V JUMP  of SAR ADC/DAC circuit  300  can be determined as follows. The voltage V X  can be represented by the following equations when all of the LSB capacitors C LX0 -C LX(K-1)  are coupled to the positive reference voltage VRP (i.e., in logic ‘1’ states), and all of the MSB capacitors C MX0 -C MX(M-1)  are coupled to the negative/ground reference voltage VRN (i.e., in logic ‘0’ states). Note that the compensation capacitor C CX  is left floating under these conditions.
 
 V   LSB   =C   LSB   /C   TOT   *Vr *(2 k −1)/(2 k −1 +C   P )  Eq. (15)
 
 V   LSB   =Vr *(2 k −1)/(2 k+m −1+2 m   *C   P )  Eq. (16)
 
     Equation (16) represents the voltage V X  associated with 2 K −1 unit capacitances C. The voltage V X  associated with a single unit capacitance C can therefore be represented as follows.
 
 LSB=Vr /(2 k+m −1+2 m   *C   P )  Eq. (17)
 
Note that equations (15, (16), and (17) are identical to equations (4), (5) and (11), above.
 
     The voltage V X  can be represented by the following equations when all of the LSB capacitors C LX0 -C LX(K-1)  are coupled to the negative/ground reference voltage VRN (i.e., in logic ‘0’ states), the MSB capacitor C MX0  is coupled to the positive reference voltage VRP (i.e., in a logic ‘1’ state), and the remaining MSB capacitors C MX1 -C MX(M-1)  are coupled to the negative/ground reference voltage VRN (i.e., in logic ‘0’ states). Under these conditions, switch S CX  connects the compensation capacitor C CX  to the negative/ground reference voltage VRN, thereby effectively enabling this compensation capacitor C CX . In the described embodiments, the capacitance of compensation capacitor C CX  (and compensation capacitor C CY ) is designated C*C C , wherein C is the unit capacitance.
 
 V   MSB   =C /( C   TOT   +C*C   C )* Vr   Eq. (18)
 
 V   MSB   =Vr *(2 k   +C   P )/(2 k+m −1+2 m   *C   P +2 K   C   C   +C   C   C   P )  Eq. (19)
 
     The term C C C P  is a relatively small value, and can therefore be ignored, resulting in the following equation.
 
 V   MSB   =Vr *(2 k   +C   P )/(2 k+m −1+2 m   *C   P +2 K   C   C )  Eq. (20)
 
For purposes of simplification, the following substitution may be employed.
 
 A =(2 k+m −1+2 m   *C   P )  Eq. (21)
 
Using the substitution of equation (21), equation (20) may be re-written as follows.
 
 V   MSB   =Vr *(2 k   +C   P )/( A+ 2 K   C   C )  Eq. (22)
 
The jump voltage V JUMP  can then be represented by the following equations.
 
 V   JUMP   =V   MSB   −V   LSB   Eq. (23)
 
 V   JUMP   =Vr *(2 k   +C   P )/( A +2 K   C   C )− Vr *(2 k −1)/ A   Eq. (24)
 
 V   JUMP   =Vr/A *(1+( AC   P −2 2K   C   C )/( A+ 2 k   C   C ))  Eq. (25)
 
     The difference between the jump voltage V JUMP  and the voltage V X  associated with a single unit capacitance (i.e., LSB) represents the jump error voltage, which can be defined by the following equations.
 
Δ V   e   =V   JUMP   −LSB   Eq. (26)
 
Δ V   e   =Vr/A *(1+( AC   P −2 2K   C   C )/( A+ 2 k   C   C ))− Vr/A   Eq. (27)
 
Δ V   e   =Vr/A *( AC   P −2 2K   C   C )/( A+ 2 k   C   C )  Eq. (28)
 
Equation (28) may be re-written as follows.
 
Δ V   e   =LSB *( AC   P −2 2K   C   C )/( A+ 2 k   C   C )  Eq. (29)
 
Equation (29) may be represented by the following approximation.
 
Δ V   e   ≈LSB *( C   P −2 k−m   *C   C )  (30)
 
     In the described embodiment, k, m and C C  are selected such that (2 k−m *C C ) is approximately equal to C P . For example, if parasitic capacitance value C P =C, k=6, and m=6, then the compensation capacitance value C C  would be selected to be approximately equal to C. Equation (30) indicates that the compensation capacitor C CX  reduces the jump error voltage ΔV e  compared to the prior art, as long as the compensation capacitance value C C  is properly selected in view of the parasitic capacitance value C P , and the values k and m. In accordance with one embodiment, the jump error voltage ΔV e  is eliminated, such that SAR ADC/DAC circuit  300  advantageously exhibits a linear response for all SAR codes. Note that if k is less than m, then C C  can be increased to minimize ΔV e . Conversely, if k is greater than m, then C C  can be reduced to minimize ΔV e . 
     In accordance with one embodiment of the present invention, the compensation capacitors C CX  and C CY  are each replaced by series-connected capacitors.  FIG. 4  is a block diagram of an SAR ADC/DAC circuit  400 , which replaces the compensation capacitors C CX  and C CY  of SAR ADC/DAC circuit  300  with series-connected capacitors C CX1 -C CX2  and C CY1 -C CY2 , respectively. Capacitors C CX1 -C CX2  are connected in series between the MSB output node X and compensation capacitor switch S CX1 . Similarly, capacitors C CY1 -C CY2  are connected in series between the MSB output node Y and compensation capacitor switch S CY1 . The common node of capacitors C CX1 -C CX2  is labeled as node X 1 , and the common node of capacitors C CY1 -C CY2  is labeled as node Y 1 . Logic control blocks  401  and  402  control compensation capacitor switches S CX1  and S CX2 , respectively, in the manner described below. 
     It is initially noted that SAR ADC/DAC circuit  400  can operate in the same manner as SAR ADC/DAC circuit  300 . That is, logic control blocks  401  and  402  may couple compensation capacitors C CX2  and C CY2  (i.e., nodes X 1  and Y 1 ) to the various voltages VIN+, VIN−, VRN and VRP (or leave these compensation capacitors C CX2  and C CY2  in floating states) in the same manner that logic control blocks  301  and  302  couple compensation capacitors C CX  and C CY  to the various voltages VIN+, VIN−, VRN and VRP (or leave these compensation capacitors C CX  and C CY  in floating states). When operating SAR ADC/DAC circuit  400  in this manner, logic control blocks  401  and  402  leave the compensation capacitors C CX1  and C CY1  in floating states. 
     Alternately, logic control blocks  401  and  402  may leave nodes X 1  and Y 1  in floating states, such that capacitors C CX1  and C CX2  are coupled in series between the output node X and a terminal selected by switch S CX1  (and capacitors C CY1  and C CY2  are coupled in series between the output node Y and a terminal selected by switch S CY1 ). In this embodiment, series-connected capacitors C CX1 -C CX2  can be viewed as a single capacitor, which has a capacitance less than C CX2  by itself. Similarly, series-connected capacitors C CY1 -C CY2  can be viewed as a single capacitor, which has a capacitance less than C CY2  by itself. Operating SAR ADC/DAC  400  in this manner effectively reduces the compensation capacitances introduced at the output terminals X and Y. 
     Logic control blocks  401  and  402  may therefore adjust the compensation capacitances introduced at the output terminals X and Y, by controlling the operation of switches S CX1  and S CY1 . Thus, the compensation capacitances may be adjusted, as necessary, to more effectively cancel the jump error voltage ΔVe. 
     In accordance with yet another embodiment, logic control blocks  401  and  402  may operate compensation capacitor switches S CX1  and S CY1  such that nodes X 1  and Y 1  are coupled to receive the respective input signals VIN+ and VIN− during a sample phase (and compensation capacitors C CX1  and C CY1  are left floating during this sample phase). After the sample phase is complete (i.e., during a hold/compare phase), logic control blocks  401  and  402  leave nodes X 1  and Y 1  in floating states, such that capacitors C CX1  and C CX2  are coupled in series between the output node X and a terminal selected by switch S CX1  (and capacitors C CY1  and C CY2  are coupled in series between the output node Y and a terminal selected by switch S CY1 ). In this configuration, series-connected capacitors C CX1 -C CX2  can be viewed as a single capacitor, which has a capacitance less than C CX2 . Similarly, series-connected capacitors C CY1 -C CY2  can be viewed as a single capacitor, which has a capacitance less than C CY2 . 
     The hold/compare phase proceeds in the same manner described above in connection with SAR ADC/DAC  300 . That is, if logic control block  401  determines that LSB switches S LX0 -S LX(K-1)  all receive digital signals representative of logic ‘0’ values, then logic control block  401  causes compensation capacitor switch S CX1  to couple compensation capacitor C CX1  to the negative/ground voltage VRN (and leave the common node X 1  floating), thereby coupling the compensation capacitors C CX1  and C CX2  in series between the MSB output node X and the negative/ground voltage VRN. 
     However, if logic control block  401  determines that one or more of LSB switches S LX0 -S LX(K-1)  receive digital signals representative of a logic ‘1’ value, then logic control block  401  causes compensation capacitor switch S CX1  to leave both compensation capacitor C CX1  and common node X 1  in a floating state, effectively de-coupling the compensation capacitors C CX1  and C CX2  from output node X. Logic control block  402  controls compensation capacitor switch S CY1  in the same manner that logic control block  401  controls compensation capacitor switch S CX1 . 
     Although  FIGS. 3 and 4  illustrate differential SAR ADC/DAC circuits  300  and  400 , respectively, it is understood that the present invention can also be applied to single-ended SAR ADC/DAC circuits.  FIGS. 5 and 6  are block diagrams of single ended SAR ADC/DAC circuits  500  and  600 , respectively, in accordance with alternate embodiments of the present invention. Because SAR ADC/DAC circuits  500  and  600  are similar to SAR ADC/DAC circuits  300  and  400 , similar elements in  FIGS. 3 ,  4 ,  5  and  6  are labeled with similar reference numbers. 
     The present invention can also be applied to charge scaling digital-to-analog converters (DACs).  FIG. 7  is a block diagram of a differential charge scaling DAC  700  in accordance with one embodiment of the present invention. Similar elements in  FIGS. 3 and 7  are labeled with similar reference numbers. Charge scaling DAC  700  replaces the comparator  101  of SAR ADC/DAC circuit  300  with an operational amplifier  701 , which is connected as illustrated. Charge scaling DAC  700  replaces the SARs  102   X - 102   Y  of SAR ADC/DAC circuit  300  with digital input logic blocks  702   X - 702   Y . Digital input logic blocks  702   X - 702   Y  supply digital signals to switches S LX0 -S LX(K-1) , S MX0 -S MX(M-1) , S LY0 -S LY(K-1)  and S MY0 -S MY(M-1) , which are representative of an analog output signal (OUTPUT) to be generated. Logic control blocks  301  and  302  operate in response to the digital signals provided by digital input logic blocks  702   X - 702   Y , in the manner described above in connection with  FIG. 3 . 
       FIG. 8  is a block diagram of a charge scaling DAC  800 , which replaces the logic control blocks  301 - 302 , compensation capacitor switches S CX -S CX  and compensation capacitors C CX -C CY , of charge scaling DAC  700  with logic control blocks  401 - 402 , compensation capacitor switches S CX1 -S CX2  and compensation capacitors C CX1 -C CX2  and C CY1 -C CY2 . The operation of logic control blocks  401 - 402 , compensation capacitor switches S CX1 -S CX2  and compensation capacitors C CX1 -C CX2  and C CY1 -C CY2  is described in detail above in connection with  FIG. 4 . 
       FIG. 9  is a block diagram of a single-ended charge scaling DAC  900  in accordance with yet another embodiment of the present invention. Because charge scaling DAC  900  is similar to charge scaling DAC  700 , similar elements in  FIGS. 7 and 9  are labeled with similar reference numbers. Single-ended charge scaling DAC  900  operates in a manner similar to differential charge scaling DAC  700 . 
       FIG. 10  is a block diagram of a single-ended charge scaling DAC  1000  in accordance with another embodiment of the present invention. Because charge scaling DAC  1000  is similar to charge scaling DAC  800 , similar elements in  FIGS. 8 and 10  are labeled with similar reference numbers. Single-ended charge scaling DAC  1000  operates in a manner similar to differential charge scaling DAC  800 . 
     Although the present invention has been described in connection with various embodiments, it is understood that variations of these embodiments would be obvious to one of ordinary skill in the art. For example, although the present invention has been described in connection with binary-weighted capacitors, it is understood that the present invention is equally applicable to systems that implement non-binary weighted capacitors. Thus, the present invention is limited only by the following claims.