PMOS Transponder Modulator Preventing Minority Carrier Injection
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Solution Overview
Problem
RFID transponders using NMOS modulators face functional issues due to parasitic diode activation from negative antenna swings, leading to minority carrier injection and limited dynamic range, which existing solutions like deep n-well technology attempt to address but increase production costs.
Innovation Solution
Employing a PMOS transistor with its drain and source in an n-type well within a p-type substrate, and a specialized driving circuit that provides a negative gate voltage to control the PMOS transistor, preventing electron injection and using an Anti-Negative Drift circuit to manage gate voltage after modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If an NMOS transistor is used as a modulator in a RFID transponder, then the modulator can be easily switched with available voltage range, but the parasitic diode turns on during negative antenna swings causing minority carrier injection and limited dynamic range
Solution Approach 1:
The patent inverts the conventional approach by using a PMOS transistor instead of an NMOS transistor for the modulator. This inversion changes the substrate interaction: PMOS transistors have a parasitic diode between the p-type drain and n-type well, preventing electron injection into the substrate during negative antenna swings, thus resolving the reliability issue while maintaining switching capability
Solution Approach 2:
The patent changes the electrical parameters of the modulator by selecting a different transistor type (PMOS vs NMOS) and configuring the substrate connection differently. This parameter change fundamentally alters the behavior of the parasitic diode, preventing harmful electron injection and expanding the dynamic range without sacrificing ease of operation
2Reliability
If deep n-well technology is used to isolate the NMOS modulator, then minority carrier propagation is stopped, but production costs increase due to additional masks and fabrication steps
Solution Approach 1:
Instead of using deep n-well technology to isolate the NMOS modulator, the patent inverts the approach by using a PMOS transistor in a standard n-well process. This inversion naturally prevents minority carrier injection into the substrate without requiring additional isolation structures, thereby maintaining reliability while reducing manufacturing complexity and cost
Solution Approach 2:
The patent extracts the need for deep n-well isolation technology by fundamentally changing the transistor type. The PMOS configuration inherently prevents the harmful effect without requiring the extraction or addition of complex isolation structures, simplifying the manufacturing process
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 solution effectively prevents minority carrier injection into the substrate, maintaining normal functionality across a wider dynamic range without increasing production costs, thus enhancing the operational reliability and efficiency of RFID transponders.
Implementation Method 1
The negative swing on the antenna pad can be large enough to turn this parasitic diode on. This results in the injection of electrons from the n-type drain region into the p-type substrate. Electrons become minority carriers when injected in the p-substrate.
Data Source
Figure 1~2B
Figure 3A~4
Figure 5
AI summary
The RFID transponder of the invention comprises an electronic circuit and an antenna, the electronic circuit being integrated in a p-type substrate and comprising a modulator (32) formed by a PMOS transistor whose drain, electrically connected to a pad (Ant) of the antenna, and source, connected to the ground (Gnd) of the electronic circuit, are arranged in an n-type well provided in the p-type substrate. The PMOS transistor has a gate (40) driven by a driving circuit which is arranged for providing at least a negative voltage, this negative voltage being low enough for turning on this PMOS transistor in response to a control signal (Tx) provided by a logical unit of the electronic circuit. In particular, the driving circuit comprises an inverter (50) followed by a high-pass filter formed by a series capacitor (52), connected to the gate of the PMOS transistor, and a parallel diode (54) connected between this gate and the ground, this driving circuit further comprising a current source (56) arranged between a positive supply voltage (Vdd) and the diode together with a switch (58) controlled so that it turns off when the modulator is turned on.