AN383 查看數據表（PDF） - Silicon Laboratories

零件编号

产品描述 (功能)

生产厂家

AN383

Si47XX ANTENNA, SCHEMATIC, LAYOUT, AND DESIGN GUIDELINES

Silicon Laboratories 

AN383

Optional RF shunt capacitors C5 and C6 may be placed on the left and right audio traces at the headphone

amplifier output to reduce the level of digital noise passed to the antenna. The recommended value is 100 pF or

greater, however, the designer should confirm that the headphone amplifier is capable of driving the selected shunt

capacitance.

This schematic example uses the National Semiconductor LM4910 headphone amplifier. Passive components R1–

R4 and C7–C8 are required for the LM4910 headphone amplifier as described in the LM4910 data sheet. The gain

of the right and left amplifiers is –R3/R1 and –R4/R2, respectively. These gains can be adjusted by changing the

values of resistors R3 and R4. As a general guide, gain between 0.6 and 1.0 is recommended for the headphone

amplifier, depending on the gain of the headphone elements. Capacitors C7 and C8 are ac-coupling capacitors

required for the LM4910 interface. These capacitors, in conjunction with resistors R1 and R2, create a high-pass

filter that sets the audio amplifier's lower frequency limit. The high-pass corner frequencies for the right and left

amplifiers are:

fCRIGHT = 2------------R---1--1--------C----7-- fCLEFT = 2------------R---1--2--------C----8--

With the specified BOM components, the corner frequency of the headphone amplifier is approximately 20 Hz.

Capacitor C1 is the supply bypass capacitor for the audio amplifier. The LM4910 can also be shut down by

applying a logic low voltage to the number 3 pin. The maximum logic low level is 0.4 V and the minimum logic high

level is 1.5 V.

The bill of materials for the typical application schematic shown in Figure 6 is provided in Table 12. Note that

manufacturer is not critical for resistors and capacitors.

3.3. Headphone Antenna Bill of Materials

Table 12. Headphone Antenna Bill of Materials

Designator

LMATCH

C4

D1, D2, D3

U3

R1, R2, R3, R4

C7, C8

C5, C6

R5, R6

F1, F2

C1

R7

Description

IND, 0603, SM, 270 nH, MURATA, LQW18ANR27J00D

AC coupling cap, SM, 0402, X7R, 100 pF

IC, SM, ESD DIODE, SOT23-3, California Micro Devices, CM1210-01ST

IC, SM, HEADPHONE AMP, National Semiconductor, LM4910MA

RES, SM, 0603, 20 k

CAP, SM, 0603, 0.39UF, X7R

CAP, SM, 0402, C0G, 100 pF

RES, SM, 0603, 100 k

FERRITE BEAD, SM, 0603, 2.5 k, Murata, BLM18BD252SN1D

CAP, SM, 0402, X7R, 0.1 µF

RES, SM, 0402, 10 k

Note

20

Rev. 0.8

Share Link: