Direct Conversion Receiver DC Offset Cancellation With Hybrid Servo Loop
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Solution Overview
Problem
Direct Conversion Receivers (DCRs) face significant challenges in reducing DC offset, which can dominate signal strength and cause malfunctions in digital stages due to their unique architecture, especially in WLAN environments, where conventional methods like AC coupling and high-resolution digital compensation are impractical for portable devices.
Innovation Solution
A hybrid DC offset reduction method combining a static compensator with a servo-loop feedback amplifier, using a low-resolution static compensation and two registers for amplifier gain settings, along with a gain mapping approach to condense DC offset to a smaller range, allowing on-chip implementation and fast initial acquisition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If AC coupling is used to remove DC offset, then DC offset is reduced, but signal distortion occurs and large capacitors are required
Solution Approach 1:
The patent extracts and removes only the DC offset component from the signal path using a DC block circuit, while allowing the AC signal to pass through unaffected. This selective extraction avoids the need for large capacitors that would be required for AC coupling, as the DC removal is achieved through a dedicated circuit that targets only the DC component.
Solution Approach 2:
The patent introduces a DC block circuit as an intermediary component between the LNA and the signal processing stages. This intermediary circuit specifically targets and removes DC offset without affecting the AC signal, avoiding the need for large capacitors that would be required in traditional AC coupling approaches.
2Measurement precision
If high-resolution digital compensation is used to reduce DC offset, then DC offset accuracy is improved, but chip area and power consumption increase
Solution Approach 1:
The patent replaces complex digital compensation mechanisms with a simpler analog DC block circuit. Instead of using high-resolution digital-to-analog converters and extensive digital processing circuitry, the invention uses an analog circuit approach that achieves effective DC offset removal with significantly reduced chip area and power consumption.
Solution Approach 2:
The patent employs a simple, low-cost DC block circuit that provides sufficient DC offset removal without requiring expensive high-resolution DACs or complex digital compensation hardware. The solution uses basic analog components that are inexpensive and occupy minimal chip area.
3Device complexity
If conventional DC offset cancellation is used in direct conversion receiver, then signal processing is simplified, but DC offset dominates signal strength causing malfunction
Solution Approach 1:
The patent applies preliminary DC offset removal at the early stage of signal reception, immediately after the LNA. By placing the DC block circuit in this early position, the DC offset is eliminated before it can dominate the signal strength and cause malfunction in subsequent AGC and digital processing stages, while maintaining the simplified direct conversion architecture.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively reduces both Type-I and Type-II DC offsets with a short calibration period, maintaining accurate gain feedback and DC cancellation, suitable for portable devices without the need for high-resolution DACs or extensive circuitry, ensuring stable operation even under dynamic gain adjustments.
Implementation Method 1
a servo-loop feedback amplifier to cancel the dynamic DC offset
Implementation Method 2
a static compensator to remove the static DC offset
Data Source
AI summary
A hybrid structure circuit for the cancellation of both Type-I and Type-II DC offsets. It comprises a static compensator in conjunction with a servo-loop feedback amplifier to suppress the undesired DC components present along the path of the base band after the direct conversion mixer. Two mixers are used to down convert a received RF signal directly to a base band signal with two components: in-phase and quadrature-phase. Both in-phase and quadrature-phase branches employ the same circuitry for DC offset cancellation. Miller effect is also utilized in the structure in order to implement the circuit on-chip.