DC Supply Voltage Control Circuit for Long Telephone Lines
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Solution Overview
Problem
Existing control circuits for DC supply voltage in telephone networks are not suitable for long telephone lines, as they fail to maintain adequate energy supply due to increased load resistance, leading to reduced line current below minimum thresholds.
Innovation Solution
A control device that can switch between constant line current and constant line voltage operations, using a sensing circuit, subtractor, analogue/digital converter, digital low-pass filter, and controller to generate and adjust the supply voltage, minimizing circuit complexity and external components, and requiring only one analogue/digital converter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional control circuits are used for DC supply voltage, then the circuit structure is simple, but the power supply becomes inadequate for long telephone lines due to increased load resistance
Solution Approach 1:
The control circuit dynamically switches between constant current mode and constant voltage mode based on detected line conditions. The controller monitors the actual current and compares it with the nominal current, switching operating modes accordingly to maintain adequate power supply across varying line resistances while managing circuit complexity through adaptive behavior
Solution Approach 2:
The circuit employs feedback by detecting the actual line current through the sensing resistor and comparing it with the nominal current value. The controller uses this feedback information to determine the operating mode and adjust the supply accordingly, ensuring reliable power delivery while maintaining manageable circuit complexity through intelligent control
2Reliability
If constant line current operation is used, then power supply is maintained for long lines, but the circuit requires more complex control mechanisms
Solution Approach 1:
The system dynamically adapts its control strategy based on actual operating conditions. Rather than implementing complex constant current control always, it switches to constant voltage mode when appropriate, reducing overall system complexity while maintaining reliability when needed
Solution Approach 2:
The controller changes the operating parameter (current or voltage) based on detected conditions. By switching between constant current and constant voltage modes, the system optimizes performance for different line lengths and conditions without requiring complex control mechanisms for all scenarios
3Measurement precision
If multiple analogue/digital converters are used, then conversion accuracy is improved, but the chip area increases
Solution Approach 1:
The single analogue/digital converter performs multiple functions: converting the sensed voltage from the sensing resistor, and potentially other signal conversions within the control circuit. This multi-functionality reduces the total number of converters needed, minimizing chip area while maintaining necessary measurement precision through efficient use of the available converter
Solution Approach 2:
The circuit merges the functions of multiple converters into a single converter that handles multiple conversion tasks. By combining these functions, the design achieves the necessary conversion accuracy without the chip area penalty of having separate dedicated converters for each function
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
Ensures adequate power supply to terminals connected via long subscriber lines with minimal circuit complexity, adaptability to country-specific parameters, and reduced chip area integration.
Implementation Method 1
The line current sensed by the SLIC circuit leads to a voltage drop across a resistor RSENSE
Implementation Method 2
a subtractor which, in the constant line current operation, subtracts an analogue feedback voltage dependent on an adjustable nominal direct-current value from the sensed input voltage for generating an analogue difference voltage
Implementation Method 3
an analogue/digital converter for converting the generated analogue difference voltage into a digital difference voltage value
Implementation Method 4
a digital low-pass filter for filtering a sequence of control error values out of the generated sequence of difference voltage values
Implementation Method 5
a controller for generating a control value in dependence on the filtered-out sequence of control error values
Implementation Method 6
a first digital/analogue converter which, in the constant line current operation, converts the control value in each case generated by the controller into the analogue direct voltage for supplying the terminal
Data Source
AI summary
A control device includes a circuit operable to sense an analog input voltage dependent on a line current flowing via a communication line of a terminal generate an analog difference voltage in a constant line current operation based on a difference between the sensed analog input voltage and an analog feedback voltage which depends on an adjustable nominal direct-current value and filter a sequence of control error values from a sequence of digital difference voltage values converted from the generated analog difference voltage. The circuit is further operable to convert a control value generated from the sequence of control error values in the constant line current operation to an analog direct voltage for supplying the terminal and convert the nominal direct-current value into the analog feedback voltage in the constant line current operation.