SSM2167

Data Sheet

Rev. G | Page 10 of 12

SETTING THE NOISE GATE THRESHOLD

(DOWNWARD EXPANSION)

The noise gate threshold is a programmable point using an external

−40 dBV and −55 dBV, as shown in Table 5. 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 18. It is not recommended

floor of the SSM2167 prevents the noise gate from being

lowered further without causing problems.

Table 5. Setting Noise Gate Threshold

Noise Gate (dBV)

−40

0 Ω (short to V+)

−48

1 kΩ

−54

2 kΩ

−55

5 kΩ

INPUT (dB)

1

1

r:1

VCA GAIN

Figure 18. Effects of Varying the Downward

Expansion (Noise Gate) Threshold

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 the SSM2167 is set internally to −24 dBV (63 mV rms).

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 SHUTDOWN pin (Pin 3) of the SSM2167. In this state,

the input and output circuitry of the SSM2167 assumes a high

impedance state; as such, the potentials at the input pin and the

output pin are 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 sec. 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, whereas the on-to-off settling time is less than

1 ms. The SSM2167 shutdown current is related to both temper-

ature and voltage.

PCB LAYOUT CONSIDERATIONS

Because 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 PCB that contains the IC

and its associated components. The following applications hints

should be considered for the PCB.

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 PCB runs. In

applications where an analog ground and a digital ground are

available, the SSM2167 and its surrounding circuitry should be

connected to the analog ground of the system. As a result of

these recommendations, wire-wrap board connections and

grounding implementations are to be explicitly avoided.