Differential DAC Driver Circuit for Low-Impedance Loudspeakers
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Solution Overview
Problem
Existing driver circuitry for low-impedance transducers, such as loudspeakers in headphones, faces challenges in minimizing size and power consumption, particularly in applications like wireless earbuds where space and battery life are limited, and requires efficient solutions to drive bridge-tied-loads effectively.
Innovation Solution
The proposed driver circuitry includes differential-output amplifiers and switched capacitor direct-charge-transfer digital-to-analogue converters (DACs) that eliminate the need for separate DAC and driver amplifier stages in each signal path, using a differential-output amplifier circuit to regulate the DAC outputs and provide analogue driving signals for bridge-tied-loads with impedances of 1000 ohms or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If separate DAC and driver amplifier stages are used in each signal path, then the circuit can drive the load effectively, but the circuit area and power consumption increase
Solution Approach 1:
The patent combines the driver amplifier stages into a shared differential-output amplifier circuit that serves both signal paths. Instead of having separate DAC and amplifier stages for each channel, the invention merges the amplification function into a single differential amplifier that regulates the outputs of both DACs simultaneously, thereby reducing total circuit area and power consumption while maintaining the ability to drive the bridge-tied-load effectively
2Reliability
If separate DAC and driver amplifier stages are used in each signal path, then the circuit can drive the load effectively, but the device size increases
Solution Approach 1:
The invention merges the amplification function into a single differential amplifier that serves both signal paths. The differential-output amplifier circuit with shared feedback paths consolidates what would otherwise be separate amplifier stages, significantly reducing the circuit area required while maintaining the capability to drive low-impedance bridge-tied-loads effectively
3Power
If the driver circuitry is designed for low-impedance loads, then it can drive small transducers effectively, but stability becomes more difficult to maintain
Solution Approach 1:
The patent implements feedback paths from the output nodes back to the inputs of the differential amplifier circuit. This feedback mechanism allows the circuit to automatically adjust and regulate the outputs, maintaining stability when driving low-impedance loads by correcting any deviations in real-time, thereby enabling effective driving of small transducers while preserving circuit stability
Data Source
AI summary
This application relates to driver circuitry (200) for receiving a digital input signal (D) and outputting, at first and second output nodes (203p, 203n), first and second analogue driving signals respectively for driving a transducer (101), e.g. loudspeaker, in a bridge-tied-load configuration. The driver circuitry may particularly be suitable for driving low-impedance transducers. The driver circuitry has first and second digital-to-analogue converters (201p, 201n) configured to receive the digital input signal and the outputs of the first and second digital-to-analogue converters are coupled to the first and second output nodes respectively. A differential-output amplifier circuit (202) has outputs connected to the first and second output nodes and is configured to regulate the outputs of the digital-to-analogue converters at output nodes to provide the analogue driving signals.