Empowering High-Speed Optical Communication: Application of Microgate MGHB0603OP Series Beads in Optical Module BIAS-TEE Circuit

Introduction

With the rapid development of artificial intelligence, cloud computing, and 5G technology, data centers are increasingly demanding higher data transmission rates. From 100G to 400G, and even to 800G and 1.6T optical modules, the continuous doubling of signal rates poses extremely stringent challenges to the signal integrity (SI) and power integrity (PI) of circuits.

In the transmitter optical sub-assembly (TOSA) of an optical module, the bias circuit between the laser driver and the laser (EML/VCSEL) is one of the core components. Specifically, the BIAS-TEE (bias tee) circuit is responsible for superimposing the DC bias voltage and the AC RF signal to drive the laser to operate. However, if high-frequency noise on the DC power supply enters the bias terminal directly without being filtered, it will cause the laser to generate relative intensity noise (RIN), which in turn will increase the bit error rate (BER) and even affect the opening degree of the optical eye.

As a leading enterprise in the domestic passive components field, Microgate‘s MGHB0603OP series of high-frequency magnetic beads have become an ideal choice in optical module BIAS-TEE circuits due to their excellent impedance characteristics and low DC resistance.

1. Key challenges of the BIAS-TEE circuit in optical modules

The basic structure of the BIAS-TEE circuit consists of a capacitor (for blocking DC) and an inductor/magnetic bead (for passing DC and blocking AC). In the design of high-speed optical modules, this part of the circuit faces the following main challenges:

1. Power supply noise coupling: If the switching noise generated by the DC-DC converter or LDO inside the optical module couples to the laser bias voltage, it will directly modulate the laser output, resulting in jitter.

2. High-frequency impedance matching: As the speed increases, traditional power inductors may lose their choke effect due to insufficient self-resonant frequency (SRF) at high frequencies, and may even introduce resonance peaks.

3. Space and loss constraints: The internal space of optical modules is extremely compact, requiring components with small dimensions (0201 or smaller). At the same time, the trend towards low voltage driving requires components with extremely low direct current resistance (DCR) to reduce voltage drop and heat generation.

II. Overview of Magnetics MGHB0603OP Series Bead Products

The MGHB0603OP series from Microgate is a chip ferrite bead specifically designed for high-frequency, high-reliability applications. This series has been optimized for power filtering scenarios in communication equipment and optical modules, aiming to resolve the conflict between high-frequency noise suppression and DC voltage drop.

Core Features:

Package size: 0201 (0603 metric), suitable for high-density PCB layout.

Impedance characteristics: Provides high impedance within a wide frequency band (especially in the range of 100MHz to several GHz),

Low DCR design: An optimized internal electrode structure significantly reduces DC resistance, ensuring the stability of the bias voltage.

High reliability: Meets industrial-grade temperature standards, withstands soldering thermal shock, and meets the long-term operational requirements of optical modules.

III. Application Advantages of Microgate MGHB0603OP Series Magnetic Beads in BIAS-TEE Circuit

In the design of the bias circuit for optical modules, the Magnetics MGHB0603OP series magnetic beads are typically applied in the following two key positions, serving distinct functions:

1. Noise filtering at the DC input terminal of BIAS-TEE

This is the primary application scenario for this series of magnetic beads. Before the DC power supply enters the BIAS-TEE inductor, a MGHB0603OP magnetic bead is connected in series.

Function: It constitutes a filter to block high-frequency switching noise from the power management chip from entering the sensitive laser bias terminal.

Advantages: Compared to traditional inductors, magnetic beads exhibit resistive characteristics at high frequencies, capable of absorbing noise rather than reflecting it. This avoids peak interference caused by LC resonance, resulting in a smoother power supply curve.

2. RF Choke for high-frequency BIAS-TEE

In the design of optical modules operating at specific frequencies, when the operating frequency falls within the high impedance peak region of the magnetic bead, MGHB0603OP can be directly used as the RF choke component of BIAS-TEE.

Function: Prevents radio frequency signals from leaking to the DC power supply terminal while allowing DC current to pass through.

Advantages: The 0201 package has small parasitic capacitance and high self-resonant frequency, which can support signal transmission at baud rates of 25G/50G and even higher without causing signal attenuation.

3. Comparative advantages in technical performance

Parameter indicators: Traditional power inductor, ordinary magnetic bead, Microgate MGHB0603OP

High-frequency impedance: Low (capacitive after SRF) Medium High (optimized for GHz)

DC resistance (DCR) Low Medium/High Very low (optimized voltage drop)

Noise suppression mechanism: reflection, absorption, efficient absorption

Package size: Larger, Smaller, 0201 (miniaturized)

Q-value characteristics: High Q (easy resonance), Low Q, Low Q (damped resonance)

IV. Application design suggestions

To fully leverage the performance of the MGHB0603OP series magnetic beads in optical modules, engineers are advised to consider the following points during design:

1. Impedance curve matching: Based on the noise spectrum characteristics of the optical module laser driver chip, select a specific sub-model of MGHB0603OP to ensure that its impedance peak covers the main noise frequency range (usually the DC-DC switching frequency and its harmonics).

2. Rated current margin: Although the BIAS-TEE bias current is usually not large (tens of mA to hundreds of mA), considering surge and temperature derating, it is recommended to choose a specification with a rated current that is more than 1.5 times the actual operating current to prevent impedance failure due to magnetic saturation.

3. Layout and routing: The magnetic beads should be placed as close as possible to the BIAS-TEE inductor or laser diode pins. The grounding loop needs to maintain low impedance to avoid re-coupling of filtered noise.

4. Multiple cascading: For ultra-high-speed modules such as 800G, if the suppression effect of a single magnetic bead is insufficient, multiple magnetic beads with different impedance characteristics can be cascaded to broaden the filtering frequency band.

V. Localization substitution and supply chain advantages

Amidst the current global supply chain volatility and the broader push for "autonomy and controllability", optical module manufacturers are increasingly demanding higher localization rates for core components.

Technological autonomy: Microgate Technology possesses complete intellectual property rights for ferrite material formulations and manufacturing processes. The performance indicators of the MGHB0603OP series are comparable to those of similar products from leading international brands.

Delivery guarantee: Localized production has shortened the delivery cycle, enabling rapid response to fluctuations in the demand of the optical module market.

Cost optimization: With equivalent performance, Microgate‘s products offer a more competitive cost advantage, aiding optical module manufacturers in reducing BOM costs.

Technical Support: Microgate provides application technical support that is tailored to customers, assisting optical module engineers in simulation modeling and noise reduction.

Conclusion

In the evolution of optical communication towards higher data rates and lower power consumption, the importance of power integrity management has become increasingly prominent. The Megitt MGHB0603OP series of magnetic beads, with its excellent high-frequency noise suppression capability, low DC loss, and high reliability, provides strong performance guarantees for the optical module BIAS-TEE circuit.

Choosing MGHB0603OP is not just selecting a high-performance passive component, but also adding an extra layer of assurance for the signal quality and long-term stability of optical modules. With Megitt Technology‘s continuous investment in the field of high-frequency materials, this series of products will undoubtedly play a pivotal role in the large-scale deployment of 400G/800G and 1.6T optical modules.