Introduction
The era of high-speed data transmission has arrived, with transmission interfaces continuously increasing their transfer rates. As new products support the latest standards, the most challenging issue in high-speed transmission is signal loss during transmission.
A Redriver, a type of Repeater IC, is primarily used to enhance and strengthen signals. Through the Redriver's equalization (EQ), flat-gain (FG), and swing adjustment functions, signal enhancement can be achieved. This ensures signal integrity at the interface, allowing the receiver to correctly identify and transmit stable signals, reducing error rates and improving signal completeness and reliability.
The NB7NQ621M is a Redriver that supports both HDMI 2.1® and DisplayPort™ 1.4a interfaces. It supports four differential signal pairs with a transmission rate of up to 12 Gbps. It allows for hardware adjustment (pin-strapping) or software adjustment (I2C) of receiver equalization (EQ) and flat-gain (FG), with up to 15 dB EQ (at 6 GHz).
Customer Circuit Diagram
Issue Description
The customer applied the Redriver in DP1.4a mode for compatibility testing and found a failure in Test 3.3.
Compared to HDMI, DisplayPort is less commonly used in consumer products and is more focused on the IT industry. However, compatibility issues still need attention. If compatibility tests are not passed, it may result in Device A functioning while Device B does not, causing engineers to spend significant time troubleshooting. Conversely, passing compatibility tests can prevent such issues and reduce unnecessary complications.
Analysis
Test 3.3 Pre-emphasis involves pre-enhancing the first bit of a continuous signal. The higher the Pre-emphasis Level, the greater the enhancement ratio.
Based on testing experience, Pre-emphasis failures can be addressed by reducing EQ and FG settings.
Current settings: FG: L / OS: R / EQ1: F / EQ0: L
FG: 1.1 dB, OS: 1200 mV, EQ: 6.1 dB
Suggested modifications:
Set FG: L / OS: R / EQ1: F / EQ0: L
FG: -0.5 dB, OS: 1200 mV, EQ: 4.8 dB
After modifying FG and EQ settings, the compatibility test was successfully passed.
Conclusion
The NB7NQ621M not only allows external resistor settings to adjust FG, EQ, and Output Swing for flexible adaptation to various PCB trace lengths and signal enhancement applications, but it also supports I2C digital control for quick adjustments, enabling products to pass certification efficiently.
Reference Document
https://www.onsemi.cn/products/signal-conditioning-control/redrivers/nb7nq621m