ZTE Corporation ZM8300G Benutzerhandbuch
ZTE ZM8300G Module Hardware User Manual
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Figure 3-14 Circuit Recommended for the USB Interface
To ensure that the designed USB interface complies with USB 2.0 specifications, observe
the following guidelines:
1) Ensure that USB differential signal lines have a complete reference ground and the
impedance of PCB differential signal lines is 90 ohms.
2) Note the impact of the junction capacitor of the ESD protection device on the
high-speed USB data line. Generally, select a junction capacitor with the capacitance less
than 2 pf, and locate the ESD protection device near the USB interface.
3) Ensure that USB differential signal lines are far away from crystal lines, oscillator lines,
and RF signal lines and have a complete reference ground plane both above and below. In
addition, ensure that USB differential signal lines in the same layer are protected by ground
cables.
3.10 Audio Interfaces
3.10.1 Pin Description
The ZM8300G module provides PCM and I
2
S digital audio interfaces, which share the same
physical interface. That is, the ZM8300G module supports only the PCM interface or the I
2
S
interface at a time. The audio interface can be connected to a voice CODEC chip, for example,
WCD9330 from Qualcomm. Table 3-10 describe the two types of audio interfaces.
Table 3-10 Description of Digital Audio Interfaces
Pin
PCM
Description
I2S
Description
26
PCM_DIN
PCM audio data RX signal
I2S_D0
I
2
S audio data D0 signal
27
PCM_DOUT
PCM audio data TX signal
I2S_D1
I
2
S audio data D1 signal
28
PCM_CLK
PCM audio clock signal
I2S_SCLK
I
2
S audio clock signal
29
PCM_SYNC
PCM audio synchronization
signal
I2S_WS
I
2
S audio chip select
signal
3.10.2 Design Points
Both the PCM and I
2
S interfaces use digital, square wave signals. After adding a level
conversion circuit, pay attention to signal integrity. To ensure signal integrity, connect a
resistor in series and a capacitor in parallel to signal lines as impedance matching and
filtering means. When designing a PCB, note the continuity of the signal line impedance.
Figure 3-15 illustrates the recommended voice circuit. If the CODEC voice signal interface