KT6368A Case Analysis: “Bluetooth Short Range, Disconnection, and Antenna Design” – Customer Feedback and Analysis Record

 

🧠 AI Quick Insight

“Bluetooth distance short or disconnections?”

The instability of KT1328A connections beyond 20 m often traces back to three core design factors — crystal oscillator routing, RF grounding loop, and antenna clearance.

A PCB inverted-F antenna offers better performance than a ceramic antenna — if enough board space is available.

Customer Feedback

The customer used two KT1328A dual-mode Bluetooth chips (master-slave configurable):

🔹 Chip A set as the master,

🔹 Chip B set as the slave.

In their actual product testing, connections became unstable beyond 20 m.

However, during the factory sample testing stage, communication was stable — even through two walls.

The customer then provided the PCBA for further analysis.

Findings and Modification Suggestions

Key Problem Points

1. Crystal oscillator routing (bottom layer):

Do not cut out copper areas under the crystal. Keep a complete ground plane (GND) underneath to ensure stability.

2. RF trace grounding:

The RF line must have a continuous ground return path.

Discontinuity in GND causes impedance mismatch, degrading signal transmission quality.

3. Antenna clearance area:

The antenna keep-out zone is insufficient — as shown in the schematic:

Lack of proper clearance leads to reduced antenna efficiency and range.

Additional Note on Antenna Selection (Bluetooth / Wi-Fi / 2.4 GHz)

🔹 The inverted-F PCB antenna (our recommended reference design):

(1) Performs better when the board space is sufficient.

(2) Offers stronger and more stable radiation characteristics.

🔹 The ceramic antenna:

(1) Has higher energy density, making it suitable for space-constrained designs.

(2) However, its overall RF performance is slightly inferior compared to the inverted-F antenna.

Summary

In this case, the instability issue (Bluetooth disconnection beyond 20 m) when using two KT1328A master-slave chips was traced to PCB design factors rather than the chip itself.

Three main issues were identified:

1. Incomplete GND plane beneath the crystal oscillator,

2. Interrupted RF grounding path,

3. Insufficient antenna clearance.

The report also highlights antenna selection guidelines:

🔹 Choose inverted-F PCB antennas when space allows (better performance).

🔹 Use ceramic antennas only when space is limited (compact but slightly weaker signal).


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