Load Modulation Circuit Parasitic Bipolar Transistor Control
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Solution Overview
Problem
In wireless power supply systems using the electromagnetic induction method, the integration of transistors in C-DMOS processes leads to parasitic bipolar transistors being activated by discharge currents, causing high power consumption and heating due to the parasitic diode's operation as a discharge path, which results in erroneous collector current sourcing and increased heating.
Innovation Solution
The load modulation circuit incorporates load modulation controlling transistors M5 and M6, configured as N-type MOS transistors, which are synchronized with synchronous rectifying transistors to ensure controlled charge and discharge operations, avoiding the parasitic diode's discharge path and restricting discharge currents through their on-resistance, thus preventing parasitic bipolar transistor activation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a transistor is used as a switching element in a load modulation circuit using a C-DMOS process, then the transistor can be integrated into the same chip as peripheral circuits, but a parasitic bipolar transistor is activated by discharge current through the parasitic diode, causing high power consumption and heating
Solution Approach 1:
The patent extracts the problematic parasitic discharge path from the system by introducing a dedicated discharge control transistor (M6) that provides a controlled alternative discharge path for the capacitor. This separates the useful switching function from the harmful parasitic conduction, eliminating the unwanted activation of the parasitic bipolar transistor while maintaining integration benefits.
Solution Approach 2:
The patent introduces a discharge control transistor (M6) as an intermediary element that mediates between the capacitor and ground. This intermediary provides a controlled discharge path that prevents direct activation of the parasitic bipolar transistor through the parasitic diode, thereby reducing power consumption and heating while maintaining the integrated C-DMOS structure.
2Device complexity
If the parasitic diode serves as a discharge path for the capacitor, then the circuit is simple, but the discharge current activates the parasitic bipolar transistor, causing erroneous operation and increased heating
Solution Approach 1:
The patent extracts the harmful discharge current path from the parasitic diode by introducing a dedicated discharge control transistor (M6). This creates a separate, controlled discharge path that prevents the discharge current from activating the parasitic bipolar transistor, thereby eliminating erroneous operation of peripheral circuits while maintaining reasonable circuit complexity.
Solution Approach 2:
The discharge control transistor (M6) acts as an intermediary that controls the discharge current flow. By placing this intermediary in the discharge path, the patent prevents direct activation of the parasitic bipolar transistor, ensuring reliable operation of peripheral circuits while keeping the overall circuit structure manageable.
3Ease of operation
If the transistor is in an off state with accumulated electric charges in the capacitor, then the load modulation function is achieved, but the drain voltage drops by forward voltage or more from reference voltage, activating the parasitic diode
Solution Approach 1:
The patent introduces a discharge control transistor (M6) as an intermediary that provides a controlled discharge path for the capacitor. This intermediary prevents the drain voltage from dropping below the forward voltage threshold by managing charge discharge in a controlled manner, thereby preventing parasitic diode activation and reducing heating while maintaining load modulation functionality.
Solution Approach 2:
The patent changes the operational parameters of the capacitor discharge process by introducing controlled discharge through transistor M6. This parameter change ensures that the discharge occurs in a controlled manner rather than through uncontrolled parasitic conduction, preventing excessive voltage drops and resulting heating while maintaining the load modulation 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
This configuration effectively restricts discharge currents and prevents parasitic bipolar transistor operation, reducing power consumption and heating, while ensuring controlled impedance changes for efficient ASK communication in wireless power transfer.
Implementation Method 1
The electromagnetic inductive method uses the principle of electromagnetic induction that when an electric current is passed to one of two adjacent coils, an electromotive force is generated in the other adjacent coil with a magnetic flux which is generated as a medium
Implementation Method 2
a transistor is used as a switching element, and accumulation and discharge of electric charges to and from the capacitor are controlled
Implementation Method 3
a parasitic diode formed between the substrate and the well diffusion region of the same transistor becomes a discharge path of the capacitor
Implementation Method 4
a parasitic bipolar transistor with a near diffusion region in contact with the substrate (the diffusion region of the same conductive type as that of the well diffusion region) as a collector is operated by the discharge current by the parasitic diode
Data Source
AI summary
A load modulation circuit of an embodiment has a first element, a switch element configured to connect the first element to an end portion of a coil, a first control section configured to control an operation of the switch element, and a second control section configured to control an amount of electric charges accumulated in the first element, and the second control section discharges the electric charges accumulated in the first element when the switch element is switched to off.