UHF Receiver Mixer DC Reduction Circuit

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Solution Overview

Problem

Existing UHF transceiver receivers face challenges in rapidly and accurately reducing DC and low-frequency voltage components at the output of a mixing circuit within a short time interval defined by communication protocols without increasing thermal noise voltage, particularly in smart card interrogators with adjustable frequency ranges.

Innovation Solution

A circuit employing a controlled current source, variable-gain amplifier, and adjustable resistor in conjunction with an external capacitor, allowing for precise cancellation of DC and low-frequency components, with a phase-controlled upper frequency limit, enables rapid voltage reduction within a set time frame, ensuring stability and low noise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-generated harmful factors

If a high-pass filter with large capacitors (10 nF) is used to reduce DC and low-frequency components, then the voltage of DC and low-frequency components is reduced, but the receiver frequency range cannot be adjusted and external capacitors are required

Engineering Contradiction:

ImproveDC and low-frequency voltage componentsVSAvoidreceiver frequency range adjustability

Core Design Contradiction:

Object-generated harmful factorsVSAdaptability or versatility

Solution Approach 1:

The patent applies dynamics by making the capacitor value adjustable through switching elements. The capacitor that was previously fixed at 10 nF is now replaced with a switchable capacitor network that can dynamically change its value based on the desired frequency range, allowing the receiver to adapt to different frequency requirements while maintaining effective DC and low-frequency component reduction

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the parameter of capacitor value from a fixed 10 nF to an adjustable parameter. By implementing switching elements that can select different capacitor values, the system can modify the capacitive reactance to match different frequency ranges, thereby achieving both DC component reduction and frequency range adjustability

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If resistors Rp, Rn with much higher resistance than LRp, LRn are used in the high-pass filter, then the low-frequency limit can be adjusted, but thermal noise voltage increases

Engineering Contradiction:

Improvelow frequency limit adjustmentVSAvoidthermal noise voltage

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the resistance parameter from very high values (which cause noise) to optimized values. By carefully selecting resistor values that are not excessively high, the system achieves the required low-frequency limit adjustment while keeping thermal noise voltage within acceptable limits. The switching elements allow different resistance configurations to be selected based on frequency requirements

Inventive Principle:

Principle #35Parameter changes

3Loss of time

If the voltage of DC and low-frequency components is reduced rapidly within a short time interval, then the transient process is shortened, but the complexity of controlling the reduction accuracy increases

Engineering Contradiction:

Improvetransient process durationVSAvoidvoltage reduction accuracy

Core Design Contradiction:

Loss of timeVSMeasurement precision

Solution Approach 1:

The patent applies preliminary action by pre-configuring the capacitor and resistor values through switching elements before the transient process begins. The switching elements are controlled to establish the appropriate RC time constant in advance, allowing the voltage reduction to proceed rapidly and accurately without requiring complex real-time control during the transient phase

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements feedback control to monitor the voltage reduction process and adjust the switching elements accordingly. By measuring the actual voltage level and comparing it with the target value, the system can make precise adjustments to the capacitor or resistor switching to achieve the desired accuracy within the short time interval

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS8315585B2Method and circuit for a fast reduction in voltage of a DC component and low-frequency components at a mixing circuit output in a receiver of a UHF transceiver

Publication Date: 2012.11.20 STMICROELECTRONICS INT NV

AI summary

A difference between an output current signal (mos) of the mixing circuit (MC) and a current from a controlled current source (CCS) is conducted to an input of an operational amplifier (A). A control voltage (cv) for said current source is a voltage at the output of the operational amplifier (A) being filtered by a low-pass filter, whose limiting frequency equals a low frequency limit of the modulation signal in the received signal (rs). The method is speeded up in that the limiting frequency of the low-pass filter is increased by two to three orders of magnitude at the beginning and is gradually lowered to said value. A rather short time duration of the transient process is achieved so that the working point with a low voltage of the DC component and low-frequency components is set at least five times faster than so far.