Voltage Divider Circuit for Field Strength Detection
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Solution Overview
Problem
Existing methods for determining field strength information, such as RSSI, suffer from insufficient spatial resolution, especially at close distances, and alter the load on antenna circuits, affecting impedance and transmission in inductive coupling scenarios, particularly in passive transponder systems used for contactless data transmission and access control.
Innovation Solution
A method and circuit arrangement using a voltage divider circuit with multiple nodes and a constant resistance value, where the input voltage is varied by selecting a divider node based on a comparison with a reference voltage, allowing field strength determination through a value table, maintaining constant input resistance and avoiding changes in antenna circuit load, and employing a non-linear functional relationship between field strength and distance to ensure uniform spatial resolution across all distances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the resistance of the voltage divider is changed by connecting or disconnecting resistance branches in a complex parallel circuit, then the output voltage can be adapted to the reference voltage, but the spatial resolution becomes insufficient at small distances and the total resistance changes depending on the selected parallel resistance
Solution Approach 1:
The voltage divider circuit is segmented into multiple fixed resistance branches connected in parallel, each branch being selectively connected or disconnected based on the required voltage division ratio. This segmentation allows for discrete, controlled resistance changes without requiring complex dynamic reconfiguration of the entire circuit.
Solution Approach 2:
The circuit transitions from a static fixed-resistance voltage divider to a dynamic configuration where resistance branches can be selectively connected or disconnected based on the received signal strength. This dynamic adjustment enables the circuit to adapt to different measurement conditions while maintaining simplicity through predefined discrete states.
2Measurement precision
If the total resistance changes depending on the selected parallel resistance, then the output voltage can be adjusted, but the load on the upstream antenna circuit changes, affecting the impedance of the antenna circuit and the transmission circuit of the transmitter
Solution Approach 1:
Multiple resistance branches with predetermined values are pre-configured in parallel within the voltage divider circuit. The selection of which branches to activate is determined in advance based on the expected signal strength range, allowing the circuit to jump directly to the appropriate resistance configuration without transient changes that would affect antenna impedance stability.
Solution Approach 2:
The circuit changes the resistance parameter of the voltage divider by selectively activating different combinations of parallel resistance branches. Each branch has a predetermined resistance value that corresponds to a specific signal strength range, enabling discrete parameter changes that minimize impact on the antenna circuit's impedance characteristics.
3Device complexity
If a fixed amplification factor is used in the operational amplifier, then the circuit is simple, but the spatial resolution is very different depending on the distance, particularly insufficient at small distances
Solution Approach 1:
The circuit employs feedback through the voltage divider configuration where the output voltage is continuously compared with the reference voltage. Based on this feedback, the control unit adjusts which resistance branches are connected, creating a closed-loop system that maintains measurement accuracy across different distances while keeping the operational amplifier itself simple.
Solution Approach 2:
The solution moves the complexity from the operational amplifier's gain control (one dimension) to the voltage divider's resistance configuration (another dimension). By using multiple discrete resistance branches in parallel, the circuit achieves fine-grained control of the input voltage to the operational amplifier, enabling precise spatial resolution without complicating the amplifier itself.
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 precise and efficient determination of field strength and distance with uniform spatial resolution, low power consumption, and stable antenna circuit load, suitable for passive transponders, allowing for adaptable data rates and extended communication range.
Implementation Method 1
an input voltage for an operational amplifier is generated from a received signal by means of an input resistor designed as a voltage divider circuit
Implementation Method 2
an output voltage is generated with a fixed amplification factor
Implementation Method 3
an input voltage for an operational amplifier is generated from a received signal by means of an input resistor designed as a voltage divider circuit
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A method for obtaining field strength information from a received electromagnetic signal using a receiver, wherein in the receiver an input voltage for an operational amplifier is generated from the received signal by means of an input resistor configured as a voltage divider circuit, and the operational amplifier generates an output voltage by means of a fixed gain factor. The input voltage is varied until the output voltage lies within a predetermined interval including the value of the reference voltage, wherein the input voltage is tapped at the voltage divider circuit, and to vary the input voltage at the voltage divider circuit, which has a plurality of divider nodes and a constant resistance value, a divider node is selected and a partial voltage is tapped.The field strength value received by the receiving unit is determined by comparing a quantity assigned to the selected divider node.