Semiconductor Voltage Clamping Circuit Using Bipolar Transistor Vbe Difference
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional techniques for clamping the voltage of an n-type semiconductor region, such as using a Schottky diode, may not be available or can cause parasitic lateral NPN transistors to turn on due to high series resistance and forward voltage, leading to ineffective voltage clamping.
Innovation Solution
A clamping circuit utilizing a current mirror and bipolar transistors, where the difference in base-emitter junction voltages of these transistors defines the voltage at which the n-type region is clamped, without relying on Schottky transistors, and includes current limiting resistors to manage current flow and ensure proper startup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Schottky diode is used to clamp the n-type region voltage, then the voltage clamping function is provided, but the Schottky diode may not be available or may have high series resistance and forward voltage causing parasitic transistor activation
Solution Approach 1:
The patent changes the clamping mechanism from relying on Schottky diode forward voltage to using the difference in base-emitter voltages of bipolar transistors. By utilizing the Vbe difference parameter (typically around 60mV at room temperature) instead of the Schottky forward voltage, the clamping voltage is precisely controlled without activating parasitic transistors. The clamping voltage is defined as Vclamp = Vbe(Q1) - Vbe(Q2), where Q1 and Q2 are bipolar transistors with carefully selected emitter areas to achieve the desired Vbe difference.
2Loss of energy
If a current limiting resistor is placed between the n-type region and the node that may pull it below ground, then current limiting is provided, but the combination with Schottky diode still results in insufficient voltage clamping
Solution Approach 1:
The patent introduces bipolar transistors Q1 and Q2 as intermediary elements between the n-type region and ground, replacing the direct Schottky diode connection. These transistors act as active mediators that precisely control the voltage at the n-type region through their base-emitter voltage characteristics, achieving reliable voltage clamping without the limitations of passive Schottky diode-resistor combinations.
3Reliability
If Schottky diode with high forward voltage is used, then voltage clamping is provided, but the n-type region is clamped at voltage sufficiently below ground potential causing parasitic transistor to turn on
Solution Approach 1:
The patent fundamentally changes the voltage reference parameter from Schottky forward voltage (typically 0.3-0.5V) to the difference in bipolar transistor base-emitter voltages (typically 60mV). This parameter change enables precise control of the clamping voltage to be just above ground potential, preventing parasitic transistor activation while maintaining effective voltage clamping functionality.
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
Effectively clamps the voltage of an n-type semiconductor region at or near ground potential, preventing parasitic transistor activation and ensuring stable operation by controlling the voltage through the ratio of transistor areas and current mirroring, thus avoiding the limitations of Schottky diode-based systems.
Implementation Method 1
The difference between the base-emitter junction voltages of the first and second bipolar transistors defines the voltage at which the n-type region is clamped
Implementation Method 2
The current mirror receives a first current and supplies a second current in response
Data Source
AI summary
A clamping circuit clamps a voltage received by an n-type semiconductor region without using a Schottky transistor. The clamping circuit includes a current mirror as well as first and second bipolar transistors. The current mirror receives a first current and supplies a second current in response. The first current is received by the first bipolar transistor, and the second current is received by the second bipolar transistor. The difference between the base-emitter junction voltages of the first and second bipolar transistors, in part, defines the voltage at which the n-type region is clamped. To start-up the circuit properly, current is withdrawn from the base/gate terminals of the transistors disposed in the current mirror. The circuit optionally includes a pair of cross-coupled transistors to reduce the output impedance and improve the power supply rejection ratio.