String DAC charge boost system and method

#The present invention relates to string digital-to-analog converters (DACs), in particular, to charge boosting in string DACs.

#String DACs convert a digital word into a corresponding analog signal. Generally, string DACs of single string type include a series connected resistor string and are used for low to moderate resolution. Dual-string DACs have been made with the impedance of the second string unit resistor significantly higher than the impedance of the first string unit resistor to reduce the loading effect to an acceptable level. Dual stage DACs also have used voltage buffers to buffer an intermediate output voltage from the first stage DAC to the second stage DAC, which also may employ a string DAC architecture.

#Dual-string DACs typically include two series connected resistor strings and two switch networks respectively for each resistor string. The output of the first resistor string, which is typically used for converting the most significant bits (MSBs) of the digital word, is coupled to the input of the second resistor string, which is used for converting the least significant bits (LSBs) of the digital word.

#FIG. 1(a) illustrates a fast glitch in a simplified dual-string DAC.

#FIG. 1(b) illustrates a slow glitch in a simplified dual-string DAC.

#FIG. 2(a) illustrates a DAC system with charge boosting according to an embodiment of the present invention.

#Embodiments of the present invention may provide string DAC. The string DAC may include an impedance network comprising a first and second impedance strings. The string DAC may also include a set of switches to couple a first voltage across the first impedance string to the second impedance string in a first code configuration and to couple a second voltage across the first impedance sting to the second impedance string in a second code configuration. Further, the string DAC may include a charge boost circuit to inject a boost charge into the impedance network during a transition between the first code configuration and the second code configuration.

#Embodiments of the present invention may provide string DAC. The string DAC may include an impedance network comprising a first and second impedance strings. The string DAC may also include a set of switches to couple a first voltage across the first impedance string to the second impedance string in a first code configuration and to couple a second voltage across the first impedance sting to the second impedance string in a second code configuration. Further, the string DAC may include a charge boost circuit to inject a charge after a transition between the first code configuration and the second code configuration.

#Embodiments of the present invention may provide a method of converting two digital signals into respective analog signals. The method may include converting a first digital signal into a first analog signal using a multi-string DAC, converting a second digital signal into a second analog signal using the multi-string DAC, and injecting a boost charge signal into the multi-string DAC during a transition between the first and second digital signal conversions.