Segmented R-DAC Capacitor Compensation for High-Frequency Linearity
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Solution Overview
Problem
Segmented R-DACs face challenges in maintaining linearity due to parasitic capacitances and signal-dependent current loads, which cause distortion, especially at high frequencies and varying input codes.
Innovation Solution
The introduction of discrete capacitors with controlled capacitance ratios and the use of replica DACs with mapping logic to stabilize the reference current, minimizing the impact of parasitic capacitances and variable current loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If segmented R-DACs use separate DACs for MSBs and LSBs to reduce the number of resistors, then area consumption is reduced, but linearity deteriorates due to parasitic capacitances and signal-dependent current loads
Solution Approach 1:
Capacitors are introduced as intermediary elements to compensate for parasitic capacitances. Specifically, a first capacitor is coupled between the output of the first DAC and the output of the second DAC, and a second capacitor is coupled between the output of the second DAC and ground, with the second capacitor having a capacitance value that is a predetermined multiple (e.g., 2N-1 times) of the first capacitor. These capacitors act as mediators to cancel out the harmful parasitic effects and improve linearity.
Solution Approach 2:
The invention changes the electrical parameters of the circuit by introducing capacitors with specifically designed capacitance values. The ratio of capacitance values between the second capacitor and first capacitor is set to a predetermined multiple (such as 2N-1) to optimize the compensation effect and achieve the desired linearity improvement while maintaining the segmented architecture benefits.
2Productivity
If segmented R-DACs operate at high frequencies to improve productivity, then conversion speed is improved, but linearity deteriorates due to increased impact of parasitic capacitances
Solution Approach 1:
The capacitors serve as frequency-dependent intermediaries that become increasingly effective at higher frequencies. By coupling the first capacitor between the MSB DAC output and LSB DAC output, and the second capacitor from LSB DAC output to ground with appropriate capacitance ratios, the circuit compensates for parasitic effects that worsen with frequency, enabling high-speed operation while maintaining linearity.
3Manufacturing precision
If replica DACs with mapping logic are added to stabilize reference current, then linearity is improved, but device complexity increases
Solution Approach 1:
Replica DACs are introduced as simplified copies of the main DAC segments. These replica DACs replicate the essential functionality and parasitic characteristics of the MSB and LSB DACs, allowing them to generate compensation signals that stabilize the reference current. The mapping logic circuits translate the digital input codes into appropriate compensation codes for the replica DACs, achieving linearity improvement through current stabilization without requiring complete duplication of the complex DAC structures.
Data Source
AI summary
Various embodiments of a segmented R-DAC are disclosed. In one embodiment, a segmented R-DAC includes first and second DACs arranged to receive most and least significant bits, respectively. The segmented R-DAC also includes a first capacitor coupled between an output of the first DAC and an output of the second DAC, and a second capacitor coupled between the output of the second DAC and a ground node. The capacitance of the second capacitor has a value that is a predetermined multiple of the capacitance value of the first capacitor.