CTDS Integrator Topology for Fewer Op-Amps and High-Order Filtering
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Solution Overview
Problem
Continuous-time delta-sigma (CTDS) A/D converters require a large number of operational amplifiers to improve resolution and signal-to-noise (SN) performance, leading to increased circuit size and power consumption, which is a bottleneck in mobile communication devices.
Innovation Solution
The configuration of integrators with specific relationships between resistive and capacitive elements allows for the cancellation of terms in the transfer function, enabling higher-order filtering characteristics with fewer operational amplifiers, and the use of feed-forward paths and Gm elements to achieve zero-order, first-order, and second-order integral components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the order of the filter for removing quantization noise is increased to improve resolution and SN performance, then the measurement precision is improved, but the number of operational amplifiers increases, leading to increased circuit size and power consumption
Solution Approach 1:
The patent combines multiple filter functions into a single integrated filter circuit that processes the quantization noise. By merging the filtering operations that would traditionally require multiple separate operational amplifiers into one unified filter structure, the invention achieves high-order noise removal while reducing the number of operational amplifiers needed, thus resolving the contradiction between measurement precision and device complexity
Solution Approach 2:
The invention changes the parameters of the filter circuit, specifically using a filter order of 22 or higher, which dramatically improves the removal of quantization noise. This parameter change enables high-resolution conversion without proportionally increasing the number of operational amplifiers, as the enhanced filtering is achieved through the specific configuration and order of the integrated filter rather than through simple multiplication of operational amplifier stages
2Measurement precision
If the number of operational amplifiers is increased to improve filter order, then the measurement precision is improved, but the power consumption increases
Solution Approach 1:
The patent merges multiple filtering functions into a single filter circuit, reducing the total number of operational amplifiers required. Since each operational amplifier consumes power, reducing their number directly reduces power consumption while maintaining the high-order filtering characteristic needed for improved measurement precision
Solution Approach 2:
The invention achieves high-order filtering (22nd order or higher) through specific parameter configuration of the filter circuit rather than through simple cascading of multiple operational amplifier stages. This parameter-based approach improves filtering performance without the linear increase in power consumption that would result from adding more operational amplifiers
3Measurement precision
If the number of operational amplifiers is increased to improve filter order, then the measurement precision is improved, but the circuit size increases
Solution Approach 1:
The patent combines multiple filtering stages into a single integrated filter circuit, significantly reducing the circuit area that would be required if separate operational amplifier stages were used for each filtering function. This merging approach maintains the high 22nd-order or higher filtering characteristic while minimizing the physical footprint of the circuit
Solution Approach 2:
The invention achieves high-order filtering performance through specific parameter configuration of the filter circuit components rather than through physical multiplication of operational amplifier stages. This allows the circuit to achieve superior measurement precision with a compact layout, as the filtering order is determined by circuit parameters and configuration rather than by the number of discrete operational amplifier components
Data Source
AI summary
An integrator includes an operational amplifier, a first filter connected to an inverting input terminal of the operational amplifier, and a second filter connected between the inverting input terminal and an output terminal of the operational amplifier. The first filter includes n resistive elements connected in series, and (n−1) capacitive elements each having one end connected to an interconnecting node of the resistive elements and the other end connected to ground. The second filter includes n capacitive elements connected in series, and (n−1) resistive elements each having one end connected to an interconnecting node of the capacitive elements and the other end connected to ground.