Voltage-Sampling RF Receiver for LO Leakage Suppression
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Solution Overview
Problem
RF receivers face challenges in tolerating strong out-of-band interference and local oscillator leakage, which often require bulky and costly SAW filters and low noise amplifiers, respectively.
Innovation Solution
A voltage sampling RF receiver circuit with a feedback loop and impedance control using a second mixer stage and feedback resistor to suppress local oscillator leakage, eliminating the need for a low noise amplifier and enabling impedance matching directly at the input stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a passive mixer driven by 25%-duty cycle oscillator is used as the first stage, then the need for a low noise amplifier is avoided and device complexity is reduced, but local oscillator leakage to the antenna occurs and may violate regulations
Solution Approach 1:
The patent implements a feedback loop that samples the RF input signal through a second array of switches controlled by the same local oscillator signals. This feedback path allows the system to detect and compensate for local oscillator leakage, enabling the removal of the low noise amplifier while maintaining regulatory compliance through active leakage cancellation
Solution Approach 2:
The patent changes the operational parameters by using voltage sampling with 25%-duty cycle local oscillator signals instead of continuous amplification. This parameter change enables the passive mixer approach that reduces device complexity while the feedback mechanism adjusts sampling timing and voltage levels to suppress leakage
2Reliability
If a low pass filter is placed after the mixer, then out-of-band linearity is improved, but the filter may not provide sufficient isolation for impedance matching
Solution Approach 1:
The feedback loop provides an alternative impedance matching mechanism that replaces the need for complex filter designs. By sampling the RF input and feeding it back through the same mixer stage, the system achieves proper input impedance matching without relying solely on the low pass filter's isolation properties
Solution Approach 2:
The low pass filter serves multiple functions: it provides out-of-band rejection for improved linearity while also working in conjunction with the feedback loop for impedance matching. The same filter structure is used for both filtering and matching purposes, reducing overall device complexity
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
The solution achieves superior out-of-band linearity and reduced component count by directly coupling the RF input to the mixer stage, while effectively suppressing local oscillator leakage through a feedback loop and DC bias voltage adjustments.
Implementation Method 1
a feedback resistor which couples the second mixer stage output to the RF input
Implementation Method 2
the RF input is sampled onto a respective low pass filter capacitor
Implementation Method 3
a passive mixer driven by 25%-duty cycle oscillator as the first stage
Implementation Method 4
generate an Intermediate frequency ('IF') output, based on the difference between the local oscillator frequency and the RF frequency
Implementation Method 5
A capacitor arrangement providing a low pass filter function is between the passive mixer and the amplifier stage
Implementation Method 6
The amplifier stage implements intermediate frequency amplification, and generates the I and Q differential signals
Data Source
AI summary
A voltage sampling RF receiver in which an impedance control circuit controls the input impedance, by using a mixer stage which generates a feedback voltage, which is coupled to the RF input by a feedback resistor. A biasing arrangement can be used to adjust the feedback path so that local oscillator leakage signals are suppressed.