Microchip Technology AC164129 数据表
Audio PICtail
™
Plus Daughter Board User’s Guide
DS70297A-page 14
© 2007 Microchip Technology Inc.
2.2.1
Line/Microphone Input Phone Jack (J1)
2.2.2
Line/Microphone Input Select Jumper (J8)
2.2.3
Line/Microphone Pre-Amplifier (U4:A)
EQUATION 2-1:
INPUT PRE-AMPLIFIER GAIN
See Figure A-2 for the complete schematic of the Line/Microphone Pre-Amplifier.
2.2.4
Anti-Aliasing Low-Pass Filter (U4:C)
The Anti-Aliasing Low-Pass Filter uses one of the four operational amplifiers on the
MCP6024 quad op amp IC (U4). The output of the Line/Microphone Pre-Amplifier
(Ref 22) uses an anti-aliasing low-pass second-order Sallen-Key structure to filter the
signal and provide a cut-off frequency of 3300 Hz.
See Figure A-3 for a schematic of the Anti-Aliasing Low-Pass Filter.
MCP6024 quad op amp IC (U4). The output of the Line/Microphone Pre-Amplifier
(Ref 22) uses an anti-aliasing low-pass second-order Sallen-Key structure to filter the
signal and provide a cut-off frequency of 3300 Hz.
See Figure A-3 for a schematic of the Anti-Aliasing Low-Pass Filter.
2.2.5
Microphone Gain Control (R29)
See Figure A-2 for the complete schematic of the Line/Microphone Pre-Amplifier.
2.2.6
ADC Channel Select Jumper (J5)
The ADC Channel Select Jumper (Ref 3) is used to select the analog-to-digital input
channel (AN0 or AN3) on the dsPIC33F or PIC24H device on the Explorer 16
Development Board.
To use channel AN0, place the jumper between pins 2 and 3 on the ADC CH SEL
header (see Figure A-2). To use channel AN3, place the jumper between pins 1 and 2.
channel (AN0 or AN3) on the dsPIC33F or PIC24H device on the Explorer 16
Development Board.
To use channel AN0, place the jumper between pins 2 and 3 on the ADC CH SEL
header (see Figure A-2). To use channel AN3, place the jumper between pins 1 and 2.
Gain
1
R29 R17
+
(
)
R3
-------------------------------
⎝
⎠
⎛
⎞
+
=
Note: Setting the gain too high can cause the output of the amplifier to saturate
and clip.