Reconfigurable Current Buffer for ADC Linearity and Bandwidth Tuning
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Solution Overview
Problem
The high input impedance of analog-to-digital converters (ADCs) when interfaced with current-mode mixers in receivers can lead to linearity issues due to the relatively high impedance, affecting the overall performance of the receiver.
Innovation Solution
A linear and bandwidth reconfigurable current buffer or amplifier is introduced as an interface between the mixer and the ADC, utilizing capacitors configured as Miller capacitors or gate-drain neutralization capacitors based on a mode signal to manage impedance and bandwidth, and incorporating variable current sources to control impedance and linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a current-mode mixer is directly interfaced with an ADC, then the circuit complexity is reduced, but the linearity deteriorates due to the high input impedance of the ADC
Solution Approach 1:
A buffer circuit is introduced as an intermediary component between the current-mode mixer and the ADC. This buffer serves as a mediator that transforms the high-impedance output of the mixer into a low-impedance signal suitable for the ADC input, thereby resolving the linearity issue without requiring a change in the mixer or ADC architecture.
Solution Approach 2:
The buffer circuit dynamically adjusts its output impedance parameter to match the ADC input requirements. By controlling the impedance transformation ratio and operating point of the buffer, the system maintains optimal linearity across varying signal conditions while preserving the simplicity of the direct mixer-ADC interface architecture.
2Adaptability or versatility
If the bandwidth of the receiver is increased to handle varying signal bandwidths, then the adaptability is improved, but the noise and distortion increase
Solution Approach 1:
The receiver incorporates dynamically adjustable filtering and amplification stages that adapt their characteristics based on the detected signal bandwidth. When narrowband signals are detected, the filter bandwidth is reduced and gain is increased; when wideband signals are present, the filter bandwidth is expanded and gain is reduced, thereby maintaining optimal signal-to-noise ratio across different operating conditions.
Solution Approach 2:
An automatic bandwidth control mechanism uses feedback from the signal detection stage to adjust the receiver parameters. The system continuously monitors the input signal characteristics and automatically configures the intermediate frequency filters and amplifiers to match the detected signal bandwidth, preventing excessive noise and distortion while maximizing adaptability to different communication standards.
Data Source
AI summary
An apparatus, including a positive input for an input differential signal; a negative input for the input differential signal; a positive output for an output differential signal; a negative output for the output differential signal; a first capacitor including a first terminal coupled to the positive output; a second capacitor including a first terminal coupled to the negative output; and a switching network configured to: couple a second terminal of the first capacitor to the negative input or a positive node based on a mode signal; and couple a second terminal of the second capacitor to the positive input or a negative node based on the mode signal.