Datasheet

AUDIO PICtail
™
PLUS DAUGHTER
BOARD USER’S GUIDE
© 2007 Microchip Technology Inc. DS70297A-page 11
Chapter 2. Hardware
This chapter provides a functional overview of the Audio PICtail Plus Daughter Board
and identifies the major hardware components. Topics covered include:
• Functional Overview
• Hardware Components
2.1 FUNCTIONAL OVERVIEW
The block diagram shown in Figure 2-1 illustrates the mainstream operation of the
Audio PICtail
Plus Daughter Board.
FIGURE 2-1: AUDIO PICtail
™
PLUS DAUGHTER BOARD BLOCK DIAGRAM
2.1.1 Speech Sampling
The incoming audio signal can come from a line input or a condenser microphone. The
speech sampling input is jumper selected (J8). The selected signal is amplified by a
non-inverting AC amplifier (Line/Microphone Amplifier) and routed to the ADC module
on the dsPIC33F or PIC24H device through an anti-aliasing filter. This second-order
Sallen-Key low-pass filter has a cutoff frequency of 3300 Hz. The ADC Channel Select
Jumper (J5) selects the input signal line (AN0 or AN3). If the input to the amplifier is a
condenser microphone, a bias voltage provides a working supply voltage for the
microphone. The line input does not require this bias voltage.
The amplifier has a variable gain from 3 dB to 23 dB, which can be adjusted to control
microphone sensitivity or boost a low line-input signal. The output of the amplifier is
biased at 1.65V.
Explorer 16
Development
Board
AN0
AN3
OC1
OC2
MICROPHONE
LINE INPUT
LOW-
PASS
FILTER
LINE OUTPUT
HEADPHONES
LINE OUTPUT
AMPLIFIER
HEADPHONE
AMPLIFIER
-1 dB to 10 dB
LINE/MIC
SELECT
ADC CHANNEL
SELECT
FILTER INPUT
SELECT
LINE/MICROPHONE
AMPLIFIER
SPI
4-Mbit
FLASH
MEMORY
CLK
VOL UP/DN
CODEC
DCI
I
2
C
DAC+
DAC-
DAC
DIFFERENTIAL
AMPLIFIER
MIC ADJ
LINE ADJ
OUTPUT
SELECT
Connector
J8
J4
J7
J5
3 dB to 23 dB
0 dB
-33 dB to 12 dB
ANTI-
ALIASING
FILTER
LOW-PASS