Electro-Optical Modulator Driver Circuit With Capacitive Voltage Swing
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Solution Overview
Problem
Current silicon ring modulators are limited by the supply voltage in achieving an optimal voltage swing for maximizing the extinction ratio and optical modulated amplitude, resulting in a higher transmitter penalty, which restricts the efficiency of optical communication systems.
Innovation Solution
A driver circuit that utilizes a level shifter circuit with capacitors to generate output voltages beyond the supply voltage limits, allowing for increased voltage swing without additional electrical supplies or control voltages, effectively enhancing the extinction ratio and optical modulated amplitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the supply voltage is increased to achieve optimal voltage swing for maximizing extinction ratio and optical modulated amplitude, then the transmitter penalty is reduced, but the device complexity and power consumption increase due to additional electrical supplies
Solution Approach 1:
The driver circuit inverts the conventional approach by using a single supply voltage and generating the required voltage swing through capacitive coupling and signal inversion. Instead of providing multiple supply voltages to achieve the voltage swing, the circuit uses a single supply and creates the differential voltage swing through the level shifter and capacitor network, effectively working backwards from the traditional multi-supply architecture.
Solution Approach 2:
The capacitor C1 acts as an intermediary element that couples the single supply voltage to the modulator while blocking DC components. This intermediary component enables the generation of the required voltage swing without directly connecting multiple supply voltages to the modulator, thus reducing device complexity while maintaining the necessary electrical characteristics.
2Reliability
If the supply voltage is increased to maximize optical modulated amplitude, then the extinction ratio is improved, but the power consumption increases
Solution Approach 1:
The circuit changes the voltage parameters dynamically through the level shifter and capacitor network. Instead of using a constantly high supply voltage, the circuit generates the required voltage swing by shifting the voltage level and utilizing capacitive coupling, thereby achieving the necessary extinction ratio with lower average power consumption.
Solution Approach 2:
The driver circuit employs periodic switching of the capacitors and transistors to generate the differential voltage swing. The periodic charging and discharging of capacitor C1, controlled by the switching transistors, creates the required voltage oscillation that drives the modulator, reducing the need for continuously high power supply.
3Device complexity
If a single supply voltage is used to reduce device complexity, then the voltage swing is limited and cannot achieve optimal extinction ratio
Solution Approach 1:
The circuit transitions from a single-voltage-dimension approach to a differential voltage dimension by using capacitive coupling. The single supply voltage is transformed into a differential voltage swing across the modulator through the level shifter and capacitor network, effectively adding a voltage differential dimension that enables optimal extinction ratio while maintaining single-supply simplicity.
Solution Approach 2:
The circuit replaces the direct electrical connection of multiple supplies with a capacitive coupling mechanism. Instead of using multiple voltage sources directly connected to the modulator, the circuit uses capacitor C1 to transfer and transform the single supply voltage into the required differential swing, substituting the direct electrical mechanism with a capacitive energy transfer mechanism.
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
The driver circuit increases the voltage swing across the electro-optical modulator, reducing the transmitter penalty and enhancing the optical modulated amplitude, thereby improving the efficiency of optical communication systems.
Implementation Method 1
a level shifter circuit (2), which comprises two capacitors (C1, C2)
Data Source
Figure 1
Figure 2
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AI summary
The present invention relates to a driver circuit (1) for driving a voltage controlled electro-optical modulator (5), by providing an output voltage (Vout) to the electro-optical modulator (5) according to an input voltage (Vin). The driver circuit (1) comprises a supply input (SP) for receiving a DC supply voltage (VDD) with a positive supply voltage level (Vdd) and an input (IN) for receiving the input voltage (Vin), wherein the input voltage (Vin) varies between a low input level and a high input level. The driving circuit further comprises a level shifter circuit (2), which comprises two capacitors (C1, C2) and is electrically connected to the input (IN), and a voltage distribution circuit (3), which is electrically connected between the level shifter circuit (2) and an output (OUT1, OUT2) of the driver circuit (1) for providing the output voltage (Vout). The level shifter circuit (2) is configured to generate, based on the input voltage (Vin) and using a first capacitor (C1) of the two capacitors (C1, C2), a first voltage (Vi) varying between the positive supply voltage level (Vdd) and a positive first level (L1) that is greater than the positive supply voltage level (Vdd). In addition, the level shifter circuit (2) is configured to generate, based on the input voltage (Vin) and using the second capacitor (C2) of the two capacitors (C1, C2), a second voltage (V2) varying between ground (GND) and a negative second level (L2). The voltage distribution circuit (3) is configured to distribute the first voltage (Vi) and the second voltage (V2) to the output (OUT1, OUT2) such that the output voltage (Vout) is variable between a positive third level (L3) that is equal to or less than the positive supply voltage level (Vdd) and a negative fourth level (L4), wherein the absolute value of the negative fourth level (L4) is greater than the absolute value of the positive first level (L1).