SSM2166_03 Datasheet, PDF (11/16 Pages) Analog Devices – Microphone Preamplifier with Variable Compression and Noise Gating

SSM2166
Figure 13a. Evaluation Board Topside Silkscreen
(Not to Scale)
Figure 13b. Evaluation Board Topside
Metallization (Not to Scale)
REV. B
Figure 13c. Evaluation Board Backside
Metallization (Not to Scale)
Signal sources are connected to the SSM2166 through a 1/8"
phone jack where a 0.1 µF capacitor couples the input signal to
the SSM2166’s +IN pin (Pin 7). As shown in Figure 12 and in
microphone applications, the phone jack shield can be option-
ally connected to the board’s ground plane (Jumper J1 inserted
into board socket pins labeled “1” and “2”) or to the SSM2166’s
VCA_R input at Pin 4 (Jumper J1 inserted into board socket pins
labeled “1” and “3”). If the signal source is a waveform or function
generator, the phone jack shield is to be connected to ground.
For ease in making adjustments for all of the SSM2166’s
configuration parameters, single-turn potentiometers are used
throughout. Optional Jumper J2 connects the COMP RATIO
pin to ground and sets the SSM2166 for no compression (that
is, compression ratio = 1:1). Optional Jumper J3 connects the
SSM2166’s POWER DOWN input to ground for normal
operation. Jumper J3 can be replaced by an open-drain logic
buffer for a digitally controlled shutdown function. An output
signal mute function can be implemented on the SSM2166 by
connecting the GAIN ADJUST pin (Pin 2) through a 330 Ω
resistance to ground. This is provided on the evaluation board
via R11 and S1. A capacitor C5, connected between Pin 2 and
ground and provided on the evaluation board, can be used to
avoid audible “clicks” when using the mute function.
To configure the SSM2166’s input buffer for gain, provisions
for R1, R2, and C2 have been included. To configure the input
buffer for unity-gain operation, R1 and R2 are removed, and a
direct connection is made between the –IN pin (Pin 6) and the
BUF_OUT pin (Pin 5) of the SSM2166.
The output stage of the SSM2166 is capable of driving
>1 V rms (3 V p-p) into >5 kΩ loads, and is externally available
through an RCA phono jack provided on the board. If the output
of the SSM2166 is required to drive a lower load resistance or
an audio cable, then the on-board OP113 can be used. To use
the OP113 buffer, insert Jumper J4 into board socket pins
labeled “4” and “5” and insert Jumper J5 into board socket pins
labeled “6” and “7.” If the output buffer is not required,
remove Jumper J5 and insert Jumper J4 into board socket pins
“5” and “7.” There are no blocking capacitors either on the
input nor at the output of the buffer.
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