Differential Pre-Driver Capacitors for Low-Jitter Transmitters
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Solution Overview
Problem
Transmitter circuit performance is limited by data jitter caused by variations in signal delay and RC time constants, leading to reduced data transmission speeds and increased costs due to high parasitic inductance in device packages.
Innovation Solution
The implementation of a differential driver circuit with programmable capacitors and current injection mechanisms to reduce effective capacitance and stabilize supply voltage, thereby minimizing data jitter and RC time constants, while maintaining low inductance bond wire packages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional transmitter circuits are used, then device packaging is simple, but data jitter increases and transmission speed is limited
Solution Approach 1:
The patent applies preliminary action by introducing a pre-driver circuit that operates before the main driver circuit. The pre-driver circuit includes a capacitor that is charged in advance and then discharged to provide a current boost during signal transitions. This preliminary charging action reduces the RC time constant and minimizes data jitter before the main transmission occurs, enabling higher transmission speeds without compromising reliability.
Solution Approach 2:
The patent changes the electrical parameters of the transmitter circuit by adding a capacitor in parallel with the driver output. This capacitor modifies the output impedance and reduces the effective RC time constant of the circuit. By changing these electrical parameters, the circuit can achieve faster signal transitions and reduce data jitter, thereby increasing transmission speed while maintaining reliability.
2Speed
If high-speed transmission is achieved, then data jitter decreases, but manufacturing cost increases due to low-inductance bond wire packages
Solution Approach 1:
The patent uses an intermediary approach by introducing a capacitor as a mediator element between the driver circuit and the transmission line. This capacitor serves as a buffer that reduces the impact of parasitic inductance from the bond wire connections. Instead of requiring expensive low-inductance bond wire packages, the capacitor compensates for the inductance effects, enabling high-speed transmission with standard packaging and reducing manufacturing costs.
Solution Approach 2:
The patent converts the harmful effect of parasitic inductance in bond wire connections into a beneficial outcome. By adding a capacitor that provides current boost during transitions, the circuit compensates for the inductance effects. This transforms the limitation of conventional packaging into an opportunity to achieve high-speed transmission without requiring expensive specialized packages, thus reducing manufacturing costs while maintaining performance.
3Speed
If capacitor is added to reduce effective capacitance, then RC time constant decreases and transmission speed increases, but device complexity increases
Solution Approach 1:
The patent merges the capacitor element with the existing driver circuit output structure. Instead of adding a completely separate complex circuit, the capacitor is integrated into the driver output stage, combining the capacitive element with the existing drive architecture. This merging approach reduces the overall device complexity compared to adding a fully independent circuit module, while still achieving the goal of reducing RC time constant and increasing transmission speed.
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 reduces data jitter and increases transmission speed without requiring low inductance bond wire packages, achieving stable signal transitions and improved transmitter performance.
Implementation Method 1
each pre-driver includes one or more capacitors, a first end of each capacitor being connected to the output of the pre-driver and a second end of each of the capacitors being connected to a sub-pre-driver circuit
Data Source
AI summary
Embodiments of the invention are generally directed to elements to counter transmitter circuit performance limitations. An embodiment of an apparatus for driving data on a differential channel including a first output terminal and a second output terminal includes a differential driver circuit; and a first pre-driver and a second pre-driver, where each pre-driver has an output, wherein the first output terminal of the apparatus is coupled to the output of the first pre-driver, and the second output terminal of the apparatus is coupled to the output of the second pre-driver, where each pre-driver includes one or more capacitors, a first end of each capacitor being connected to the output of the pre-driver and a second end of each of the capacitors being connected to a sub-pre-driver circuit.