Variable Gain Amplifier Offset Correction Without Low-Frequency Cutoff
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Solution Overview
Problem
In direct conversion radio receivers, DC offset in the IF signal is amplified, exceeding the operating voltage range, necessitating quick offset correction in variable gain amplifiers, especially in high-speed mobile communications where rapid gain changes occur, but existing methods either attenuate low-frequency signals or take too long to cancel offsets.
Innovation Solution
An offset correction circuit with a smoothing circuit for detecting DC components, an adder for feedback correction, and time constant changing means that sets a small time constant during gain changes and gradually increases it to infinity for rapid offset cancellation without cutting off low-frequency signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a small time constant is used in the offset detection circuit, then the offset cancellation speed is improved, but the low frequency component of the zero-IF signal is attenuated
Solution Approach 1:
The patent applies dynamics by making the time constant variable rather than fixed. The time constant changing means dynamically adjusts the time constant based on the VGA gain state: using a small time constant when gain changes to speed up offset cancellation, and switching to a large time constant when gain is stable to prevent low frequency signal attenuation. This dynamic adjustment resolves the contradiction between speed and signal preservation.
2Object-generated harmful factors
If a large time constant is used in the offset detection circuit, then the low frequency signal is preserved, but the time until offset cancellation increases when VGA gain fluctuates
Solution Approach 1:
The patent uses dynamics by implementing a variable time constant that adapts to system conditions. When VGA gain fluctuates, the system switches to a small time constant for rapid offset cancellation. When gain is stable, it switches to a large time constant to preserve low frequency signals. This dynamic switching resolves the time preservation contradiction.
Solution Approach 2:
The patent applies parameter changes by modifying the time constant parameter based on operational conditions. The time constant changing means adjusts this critical parameter to have small values during gain transitions and large values during stable operation, thereby optimizing both offset cancellation speed and low frequency signal preservation at different stages.
3Speed
If the VGA gain changes rapidly, then the system responds quickly to signal variations, but the offset amount changes accordingly requiring faster convergence
Solution Approach 1:
The patent applies feedback by using the detected offset information to correct the VGA output. The offset detection circuit continuously monitors the output, detects the DC offset component, and feeds this information back through the adder to cancel the offset. This feedback mechanism ensures that offset convergence keeps pace with rapid gain changes.
Solution Approach 2:
The patent uses dynamics by making the time constant adaptive to gain changes. When gain changes rapidly, the system automatically switches to a small time constant to accelerate offset detection and cancellation, ensuring the feedback loop converges quickly enough to handle the rapid gain variations without excessive delay.
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
Enables quick offset cancellation while preventing low-frequency signal attenuation, ensuring efficient data reception in high-speed mobile communications by dynamically adjusting the time constant for feedback correction.
Implementation Method 1
an integration circuit including a variable resistor and a capacitor
Data Source
AI summary
The present invention quickly detects an offset and prevents cutoff of low frequency signals. Offset detection circuits smooth an output of a variable gain amplifier at a predetermined time constant and detects the offset, which is a DC component. The detected offset is added to the input of the variable gain amplifier by an adder and the offset in the output of the variable gain amplifier is corrected. The time constant in the offset detection circuit is changed by the resistance values of the variable resistors. Then, the time constant is changed to a small time constant when the gain of the variable gain amplifier is changed and thereafter to a large time constant.