Active Filter Topology for Suppressing Out-of-Band Peaking
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Solution Overview
Problem
Sigma delta analog-to-digital converters (ADCs) in transceivers, particularly for 5G and LTE applications, face challenges in minimizing power consumption while suppressing out-of-band peaking in signal transfer functions, which leads to increased power consumption and dynamic range requirements.
Innovation Solution
An active filter with a single operational amplifier and a specific feedback and input impedance network configuration that ensures a constant numerator in the signal transfer function, eliminating peaking and allowing for lower power consumption by reducing the number of active devices needed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional active filter configurations are used in sigma delta ADCs, then filtering function is achieved, but out-of-band peaking occurs leading to increased power consumption and dynamic range requirements
Solution Approach 1:
The patent applies parameter changes by modifying the feedback network configuration to include specific RC time constants that eliminate out-of-band peaking. By carefully selecting the feedback resistor and capacitor values to create a dominant pole at the desired frequency, the filter achieves flat out-of-band response without requiring additional active devices, thus reducing power consumption while maintaining filtering functionality
Solution Approach 2:
The patent introduces a specific feedback network configuration as an intermediary element between the operational amplifier and the input. This feedback network with carefully chosen RC values acts as a mediator that shapes the frequency response to eliminate peaking, allowing the existing active devices to operate efficiently without requiring additional amplifiers or complex circuitry
2Object-affected harmful factors
If additional active devices are added to suppress out-of-band peaking, then peaking suppression is achieved, but power consumption increases
Solution Approach 1:
The patent eliminates out-of-band peaking by changing the parameters of the existing feedback network rather than adding new active devices. By adjusting the feedback resistor and capacitor values to create appropriate pole frequencies, the filter achieves flat out-of-band response using the same operational amplifier, thereby suppressing peaking without increasing power consumption
Solution Approach 2:
The patent makes the existing feedback network multi-functional by configuring it to simultaneously provide signal feedback and frequency response shaping. The same feedback components that provide operational stability also eliminate out-of-band peaking through proper RC time constant selection, eliminating the need for separate peaking suppression circuitry and reducing overall power consumption
3Reliability
If conventional filter designs are used, then basic filtering is achieved, but dynamic range requirements increase due to out-of-band peaking
Solution Approach 1:
The patent improves filtering performance and reduces dynamic range requirements by changing the feedback network parameters. By setting the feedback RC time constant to create a dominant pole at the band edge frequency, the filter achieves smooth roll-off without peaking, ensuring that out-of-band signals are attenuated predictably and reducing the dynamic range burden on subsequent ADC stages
Data Source
AI summary
An active filter and an analog-to-digital converter (ADC) configured to suppress out-of-band peaking. An active filter may include an active device configured to provide a power gain to an input signal, a feedback network configured to connect an output of the active device to an input of the active device, and an input impedance network configured to couple the input signal to the input of the active device. A combination of the feedback network and the input impedance network is configured to provide frequency response properties of the active filter such that a frequency domain signal transfer function of the active filter has a constant in numerator.