SSM2167 Datasheet, PDF (8/8 Pages) Analog Devices – Low Voltage Microphone Preamplifier with Variable Compression and Noise Gating

SSM2167
Setting the Noise Gate Threshold (Downward Expansion)
Noise gate threshold is another programmable point using an
external resistor (R_GATE) that is connected between Pin 7
(NOISE GATE THRS) and V_DD. The downward expansion
threshold may be set between –40 dBV and –55 dBV, as shown
in Table II. The downward expansion threshold is inversely
proportional to the value of this resistance: setting this resistance
to 0 Ω sets the threshold at approximately 10 mV rms (–40 dBV),
whereas a 5 kΩ resistance sets the threshold at approximately
1 mV rms (–55 dBV). This relationship is illustrated in Figure 5.
We do not recommend more than 5 kΩ for the R_GATE resistor as
the noise floor of the SSM2167 prevents the noise gate from
being lowered further without causing problems.
Table II. Setting Noise Gate Threshold
Noise Gate (dBV)
–40
–48
–54
–55
Value of R_GATE
0 Ω (short to V+)
1 kΩ
2 kΩ
5 kΩ
Rotation Point (Limiting)
Input signals above a particular level, “the rotation point,” are
attenuated (limited) by internal circuitry. This feature allows the
SSM2167 to limit the maximum output, preventing clipping of
the following stage, such as a CODEC or ADC. The rotation
point for SSM2167 is set internally to –24 dBV (63 mV rms) for
SSM2167-1 and –20 dBV (100 mV rms) for SSM2167-2.
Shutdown Feature
The supply current of the SSM2167 can be reduced to under 10 µA
by applying an active LOW, 0 V CMOS compatible input to the
SSM2167’s /SHUTDOWN Pin (Pin 3). In this state, the input
and output circuitry of the SSM2167 will assume a high imped-
ance state; as such, the potentials at the input pin and the output
pin will be determined by the external circuitry connected to the
SSM2167. The SSM2167 takes approximately 200 ms to settle
from a SHUTDOWN to POWER-ON command. For POWER-ON
to SHUTDOWN, the SSM2167 requires more time, typically less
than 1 s. Cycling the power supply to the SSM2167 can result in
quicker settling times: the off-to-on settling time of the SSM2167 is
less than 200 ms, while the on-to-off settling time is less than 1 ms.
The SSM2167 shutdown current is related to both temperature
and voltage.
PC Board Layout Considerations
Since the SSM2167 is capable of wide bandwidth operation and
can be configured for as much as 60 dB of gain, special care must
be exercised in the layout of the PC board that contains the IC
and its associated components. The following applications hints
should be considered for the PC board.
The layout should minimize possible capacitive feedback from
the output of the SSM2167 back to its input. Do not run input
and output traces adjacent to each other.
A single-point (“star”) ground implementation is recommended
in addition to maintaining short lead lengths and PC board runs.
In applications where an analog ground and a digital ground are
available, the SSM2167 and its surrounding circuitry should be
connected to the system’s analog ground. As a result of these
recommendations, wire-wrap board connections and grounding
implementations are to be explicitly avoided.
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
10-Lead MSOP
(RM-10)
0.124 (3.15)
0.112 (2.84)
10
0.124 (3.15)
0.112 (2.84)
1
6
0.199 (5.05)
0.187 (4.75)
5
PIN 1
0.0197 (0.50) BSC
0.122 (3.10)
0.120 (3.05)
0.110 (2.79)
0.112 (2.84)
0.038 (0.97)
0.043 (1.09)
0.030 (0.76)
0.037 (0.94)
0.006 (0.15)
0.002 (0.05)
0.016 (0.41)
0.006 (0.15)
6؇
SEATING
PLANE
0.011 (0.28)
0؇
0.003 (0.08)
0.022 (0.56)
0.021 (0.53)
Revision History
Location
Page
Data Sheet changed from REV. 0 to REV. A.
Edits to Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Edits to Figures 2 and 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
–8–
REV. A