Differential Current Source Circuit for DAC Noise Cancellation
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Solution Overview
Problem
Current current sources in electrical components, such as DACs and current buffers, suffer from noise issues due to transistors, which are impractical to mitigate in low-power applications like smartphones without increasing voltage supplies.
Innovation Solution
Implementing complementary current sources with MOSFETs and AC or DC coupling between them to cancel out noise currents, allowing for noise attenuation without the need for large impedances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If large impedances are built into current sources to dampen noise, then noise levels are reduced, but voltage supplies must be increased which is impractical in low-power applications
Solution Approach 1:
The patent combines a first current source and a second current source into a complementary pair where the second current source mirrors the first. By coupling their outputs differentially, the noise currents generated by transistors in each source cancel each other out, achieving noise reduction without requiring large impedances or increased voltage supplies.
Solution Approach 2:
The patent converts the harmful noise currents generated by transistors into a beneficial cancellation effect. By designing complementary current sources where transistors in the second source generate similar noise currents that are out of phase with the first source, the noise is transformed from a detrimental factor into a self-canceling phenomenon.
2Ease of operation
If transistors are used to regulate current flow in current sources, then current control is achieved, but flicker noise is introduced at low frequencies
Solution Approach 1:
The patent merges two current sources with complementary transistor configurations. The transistors in the first current source and the second current source work together in a differential arrangement, where their combined output current maintains control capability while their noise currents cancel each other, particularly effective at low frequencies where flicker noise dominates.
Data Source
AI summary
At least some embodiments are directed to a system that comprises a differential switch network comprising first and second output nodes, first and second transistors coupled to the network, and first and second resistors coupled to the first and second transistors. The DAC also comprises a voltage source coupled to the first resistor and a ground connection coupled to the second resistor. The DAC further includes a capacitor coupled to the first and second transistors and to the second resistor.