Capacitor-Switched Current Source Circuit for DAC Linearity
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Solution Overview
Problem
Switched current source circuits in digital-to-analogue converters suffer from poor linearity due to voltage changes during switching between parallel paths, and the introduction of cascode transistors improves linearity but incurs additional voltage drops and increased voltage requirements.
Innovation Solution
A switched current source circuit with capacitor switching circuitry that alternates between a biasing and an active configuration, using a capacitor to charge and then connect the load node to the current source, increasing the potential difference between voltage source nodes and enhancing linearity while minimizing additional voltage drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If cascode transistors are introduced to improve linearity, then linearity is improved, but additional voltage drops occur and voltage requirements increase
Solution Approach 1:
The capacitor is pre-charged to a first voltage level before the switching operation. This preliminary charging action ensures that when the capacitor is switched to connect to the current source, it can compensate for the voltage drops introduced by cascode transistors, thereby maintaining linearity without increasing voltage requirements
Solution Approach 2:
The capacitor acts as an intermediary element between the voltage source and the current source. By being pre-charged and then switched into the circuit, it mediates the voltage level to compensate for drops caused by cascode transistors, resolving the contradiction between improving linearity and reducing voltage drops
2Adaptability or versatility
If switching between parallel paths is performed, then current steering function is achieved, but voltage changes cause poor linearity
Solution Approach 1:
The capacitor is pre-charged to a specific voltage level before switching occurs. This preliminary action ensures that when switching between parallel paths, the capacitor can compensate for voltage changes, maintaining linearity while enabling current steering functionality
Solution Approach 2:
The capacitor's voltage parameter is changed in two stages: first charged to a first voltage level, then switched to connect to the current source where its voltage contributes to increasing the potential difference. This parameter change enables both current steering and maintains linearity
3Manufacturing precision
If capacitor is used to increase potential difference, then linearity and bandwidth are improved, but circuit complexity increases
Solution Approach 1:
The capacitor serves multiple functions: it is pre-charged to compensate for voltage drops during switching, and then switched to increase the potential difference for improving linearity and bandwidth. This multi-functionality reduces the need for additional components, thereby limiting the increase in circuit complexity while achieving the desired performance improvements
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution improves the linearity and bandwidth of the switched current source circuit by increasing the potential difference between voltage source nodes, thereby enhancing the voltage headroom and reducing the detrimental effects of additional voltage drops.
Implementation Method 1
capacitor switching circuitry comprising a load node, a capacitor and a plurality of switches configured, based on a control signal, to adopt a biasing configuration followed by an active configuration. In the biasing configuration, the load node is conductively connected to the second voltage source node to bias a voltage level at the load node, and the capacitor is connected so that it at least partly charges
Data Source
AI summary
A switched current source circuit, comprising first and second voltage source nodes; a load; a current source; and capacitor switching circuitry comprising a load node, a capacitor and a plurality of switches configured, based on a control signal, to adopt a biasing configuration followed by an active configuration, wherein in the biasing configuration, the load node is conductively connected to the second voltage source node to bias a voltage level at the load node, and the capacitor is connected so that it at least partly charges; and in the active configuration, the load node is conductively connected via the load to the first voltage source node, and via the capacitor to the current source to increase a potential difference between the first voltage source node and the load node.