Cirrus Logic CDB6422 - Manual (Page 4)

CDB6422
4 DS295DB2
1. GENERAL DESCRIPTION
The CDB6422 provides an easy interface to evalu-
ate the performance of the CS6422 echo cancelling
IC in a target system. To facilitate evaluation, the
board provides a wide selection of network inter-
facing options (analog telephone line,
µ-law/a-law
PCM data, or analog RCA jack). The analog inter-
faces support a varitey of fixed and variable gain
options to allow for easy level-matching with target
hardware. The board includes a keypad and a
DTMF generator that enable dialing on standard
analog telephone systems.
Furthermore, the board can operate from a single
+12V power supply and can be operated in a stand-
alone configuration allowing for easy testing in cel-
lular car hands-free applications.
For more information regarding the configuration
of the CS6422 device, please refer to the CS6422
data sheet.
2. HARDWARE
2.1 Powering the Board
The CDB6422 board can operate from either a
+12V supply or a +5V supply. When operating
from a +5V supply, the
µ-law/a-law codec
(MC145503) is unavailable. The board comes
shipped from the factory configured for a +12V
power supply. The power supply must be able to
supply at least 500mA of current.
For operation from a +12V supply, the on-board
voltage regulators must be selected by installing
jumpers in the appropriate places marked '+12V'.
These jumpers are labeled PWR_SEL1 through
PWR_SEL4 and are located near the bulky 3-ter-
minal voltage regulators.
If operating from a +5V supply, the jumpers should
be installed in the '+5V' setting.
When the board is properly powered, at least 4
green LEDs should be lit. These LEDs are labeled
+5VA, +5VD, +5VSPKR, and +10VD. If the
board is powered from a +5V supply, the +10VD
LED will not be lit (or will be quite dim).
2.2 Analog Configuration
At first glance the analog section of the board (the
left-most quarter) might appear dauntingly com-
plex. The jumpers select, for the most part, a series
of fixed or adjustable gains in the APO, AO, NI,
and NO signal paths. Actual system implementa-
tion is not this complex. The following text de-
scribes the jumper settings in signal path order.
2.2.1 Acoustic Input
2.2.1.1 AIN1:
The acoustic input of the CDB6422 can be derived
from an 1/8" mic jack (AIN_MIC) or a standard
RCA jack (AIN_RCA). The header AIN1 selects
the input source.
2.2.1.2 MIC_BIAS:
If the acoustic input source is a standard electret
microphone, the board can supply a bias current to
power it. The mic bias is enabled by installing the
jumper on the "ENABLED" setting of the header
called MIC_BIAS. There is a fixed 2.2k series re-
sistance (R1) between the op-amp supplying the
bias voltage and the mic input. The value of the
mic bias voltage can be adjusted by tuning the pot
labeled "BIAS" (R6).
2.2.1.3 AIN2:
AIN2 selects between the ACTIVE acoustic input
circuitry (op-amps) and a PASSIVE RC-network.
2.2.1.4 AIN3, AIN4:
AIN3 and AIN4 select the type and amount of gain
for the acoustic input circuitry. For fixed gains
(AIN4 = “0dB”, “+20dB”, or “USER”), AIN3
should be set to "FIXED". For variable gain (-
20dB to +20dB) AIN3 should be set to "VARI-
ABLE" and AIN4 should be set to "-20dB to