High-speed PCB and wireless charging solutions launch PCBA

2021-11-06

Author：Downs

How to design the characteristic impedance

In high-speed PCB design, we often perform characteristic impedance control on high-speed signal lines to optimize signal quality. What is the characteristic impedance?

1. Transmission line principle

Before introducing the characteristic impedance, let's review the basic principles of transmission lines introduced in the "Signal Integrity Video". As shown in the figure on the left, the low-frequency circuit uses the RLGC model with lumped parameters, and the high-frequency circuit on the right uses the RLGC model with distributed parameters.

Solving the transmission line calculus equation is easy for you, and I won’t introduce it here. The result of the equation is that we can get the attenuation constant, characteristic impedance, phase shift constant, etc. of the PCB transmission line. The specific meaning is described in detail in "Signal Integrity Video". Here we mainly introduce the application of PCB characteristic impedance. The following is the formula for the characteristic impedance obtained by solving the equation, but it is not very useful because you cannot know the R, L, G, and C corresponding to the unit length.

2. The influence of characteristic impedance mismatch

The characteristic impedance of the transmission line refers to the impedance corresponding to each point on the line when high-speed signals are transmitted on the PCB line. We hope that the characteristic impedance of the transmission line will not change suddenly, because a sudden change in the transmission line will cause signal reflection, which will affect the signal quality.

3. Selection of characteristic impedance

The characteristic impedance of the PCB is determined by the matching resistance ZL at the load end, depending on the specifications of various interfaces. The characteristic impedance error is mainly affected by the PCB factory process and can generally be controlled within 5%-10%. The following is a common interface PCB impedance control.

USB differential cable 90Ω

PCIE differential line 100Ω

RF single-ended transmission line 50Ω

Ordinary single-ended transmission line 50Ω

pcb board

4. PCB characteristic impedance design

At present, PCB manufacturers often use polar si9000 software to calculate characteristic impedance. Let's take a single-ended signal line as an example. There are four setting parameters: dielectric constant, dielectric thickness, line width and copper foil thickness.

Dielectric constant Er1: The dielectric constant of the sheet, generally 4.2-4.5 for FR4 sheet.

Medium thickness H1: the thickness of the sheet or PP.

Line width W1/W2: the line width of PCB wiring.

Copper foil thickness: According to the actual situation, there are 0.5/1/2 OZ and so on.

Wireless charging scheme launches PCBA

5W/7.5W/10W/15W power adaptive; built-in 32bit high-performance processor; support QI (BPP\EPP) certification, in line with WPC1.2.4 protocol; high-precision FOD algorithm; integrated Dual-Channel fully synchronous digital demodulation; support OCP/OVP/OTP; support QC2.0/QC3.0/AFC; support DPL dynamic power adjustment; support simultaneous charging of multiple devices; support function customization; support USB upgrade.

The product features are as follows:

1. Single chip 5W/10W transmitter solution

2. Suitable for Type A6/A11/A28/MP-A2 etc.

3. Passed WPC 1.2.4 certification

4. Support 10W fast charge protocol

5. The efficiency is as high as 85% fast charge, 78%

6. Integrated synchronous dual-channel all-digital demodulation circuit

7. Over temperature, over voltage, software/hardware double over current and short circuit protection

8. FOD function

9. Dynamic power lock

10. Enhanced vertex shutdown

11. Adaptive input voltage 5V/9V