AN-583
APPLICATION NOTE
One
Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106, U.S.A. • Tel: 781.329.4700 • Fax: 781.461.3113 • www.analog.com
Evaluating the
Low Voltage Microphone Preamplifier with Variable
Compression and Noise Gating
by Shawn Scarlett
Rev. D | Page 1 of 4
THE
The
evaluation board is a convenient means to
evaluate and understand the operation of the
. This
application note provides a basic explanation of how the board
is set up, and how to use it to evaluate the
. This
document is only a supplement and refers to figures contained
in the
data sheet.
This application note also contains the schematics and layout for
the
evaluation board to allow easy modification and
experimentation. Applications support is available from Analog
Devices, Inc., online at
or in the United States
at 1-800-ANALOGD or 1-800-262-5643.
BASIC CONNECTIONS AND SETUP
The
board features simple, easy-to-use connections
that allow for a broad range of experimentation. The evaluation
board is available only with the
Power and Ground
The
is optimized for operation at 3 V; however, it can
operate from a wide range of supplies. Refer to the
data
sheet for the maximum limits. The
evaluation board
can be connected to a bench power supply or two AA batteries.
Power leads must be soldered into place at JP3. Alternatively, a
header jack can be soldered to the
disconnection. The power and ground connections are critical
to the performance of the
board; therefore, ensure
proper connection.
Shutdown Connection
The low current shutdown current connection is located at the
lower part of the
evaluation board along with the
power and ground. The
board has a pull-up resistor
installed so that if no connection is made at that point, the device
operates in active mode. To enable the shutdown feature, connect
SD to ground. To perform an in-depth analysis on the shutdown
current, remove the pull-up resistor (R5). Do not leave the
shutdown pin floating. When R5 is removed, connect SD
directly to the supply or ground.
Signal Connections, Input, and Output
Signal sources can be connected to the
evaluation
board with standard 3.5 mm jacks or leads, which can be
soldered directly to the
evaluation board uses 3.5 mm stereo sockets
with the signal on the tip and the sleeve connected to the board
ground; the ring is left floating. At both jumper connections, a
ground point is available to prevent noise.
The input jack is configured for maximum versatility. By
default, it is designed for use with an electret microphone or
input source. It can be changed easily to accommodate dynamic
microphones.
ELECTRET MICROPHONES
evaluation board is configured with a 2.2 kΩ
resistor (R4) to the supply for use as a biasing resistor. It connects
directly to the signal path so that both the jack and the jumper
(JP2) can be used as input connections. Standard computer electret
microphones can be used without modification because the ring
and tip are connected internally in the microphone. The input jack
and JP2 are decoupled from the input pin via a 0.1 µF capacitor (C1).
DYNAMIC MICROPHONES
When the
evaluation board is used with a dynamic or
self-powered microphone, remove R4.
OUTPUT SIGNAL
The output jack is decoupled from the circuit via a 10 µF capacitor
(C2). The connection can be made at either JP1 or the standard
3.5 mm jack, with the signal connection to the tip of the plug.
For listening tests, the output signal can be connected directly
from the 3.5 mm jack to an RCA input on a normal audio
amplifier using a standard stereo adapter cable. In this case, use
the left (white or black) RCA connection because it corresponds
with the tip of the 3.5 mm jack. The output of the
not sufficient to drive headphones or other output transducers
without external amplification.
