SSM2166S Analog Devices Inc, SSM2166S Datasheet - Page 10

• Manufacturer Part Number: SSM2166S
• Description: IC PREAMP AUDIO MONO MIC 14SOIC
• Manufacturer: Analog Devices Inc

Specifications of SSM2166S

• Rohs Status: RoHS non-compliant
• Output Type: 1-Channel (Mono)
• Voltage - Supply: 4.5 V ~ 5.5 V
• Features: Microphone
• Mounting Type: Surface Mount
• Package / Case: 14-SOIC (3.9mm Width), 14-SOL
• Max Output Power X Channels @ Load: -

SSM2166
The performance of the rms level detector is illustrated for a
C
In each of these images, the input signal to the SSM2166 (not
shown) is a series of tone bursts in six successive 10 dB steps.
The tone bursts range from −66 dBV (0.5 mV rms) to −6 dBV
(0.5 V rms). As shown in Figure 17 and Figure 18, the attack
time of the rms level detector is dependent only on C
release times are linear ramps whose decay times are dependent
on both C
approximately 240 dB/s for a C
C
CONTROL CIRCUITRY
The output of the rms level detector is a signal proportional to
the log of the true rms value of the buffer output with an added
dc offset. The control circuitry subtracts a dc voltage from this
signal, scales it, and sends the result to the VCA to control the
gain. The gain control of the VCA is logarithmic—a linear change
in the control signal causes a decibel change in gain. It is this
control law that allows linear processing of the log rms signal to
provide the flat compression characteristic on the input/output
characteristic shown in Figure 15.
AVG
AVG
100
100
0%
0%
90
10
90
10
• • • •
• • • •
• • • •
• • • •
of 2.2 μF in Figure 17 and for a C
of 22 μF.
Figure 17. RMS Level Detector Performance with C
Figure 18. RMS Level Detector Performance with C
• • • •
• • • •
• • • •
• • • •
AVG
100mV
100mV
and the input signal step size. The rate of release is
• • • •
• • • •
• • • •
• • • •
• • • •
• • • •
• • • •
• • • •
• • • •
• • • •
• • • •
• • • •
• • • •
• • • •
• • • •
• • • •
AVG
• • • •
• • • •
• • • •
• • • •
of 2.2 μF and 12 dB/s for a
• • • •
• • • •
• • • •
• • • •
AVG
100ms
1s
of 22 μF in Figure 18.
• • • •
• • • •
• • • •
• • • •
• • • •
• • • •
• • • •
• • • •
AVG
AVG
= 2.2 μF
= 22 μF
AVG
, but the
–6dBV
–66dBV
–85dBV
–6dBV
–66dBV
–85dBV
Rev. D | Page 10 of 20
Compression Ratio
Changing the scaling of the control signal fed to the VCA
causes a change in the circuit compression ratio, r. This effect is
shown in Figure 20. The compression ratio can be set by
connecting a resistor between the COMP RATIO SET pin (Pin
10) and GND. Lowering R
as shown in Figure 19, with values of approximately 17 kΩ or
less resulting in a compression ratio of 1:1. AGC performance is
achieved with compression ratios between 2:1 and 15:1 and is
dependent on the application. A 100 kΩ potentiometer can be
used to allow this parameter to be adjusted. On the evaluation
board (see Figure 26), an optional resistor can be used to set the
compression equal to 1:1 when the wiper of the potentiometer
is at its full counterclockwise (CCW) position.
Rotation Point
An internal dc reference voltage in the control circuitry, used to
set the rotation point, is user specified, as illustrated in Figure 9.
The effect on rotation point is shown in Figure 21. By varying a
resistor, R
ROTATION SET pin (Pin 11), the rotation point may be varied
by approximately 20 mV rms to 1 V rms. From Figure 21, the
rotation point is inversely proportional to R
kΩ resistor would typically set the rotation point at 1 V rms,
whereas a 55 kΩ resistor would typically set the rotation point
at approximately 30 mV rms.
ROTATION POINT
100mV rms
300mV rms
1V rms
TYPICAL R
Figure 19. Compression Ratio vs. R
ROT PT
Figure 20. Effect of Varying the Compression Ratio
COMPRESSION
COMP
, connected between the positive supply and the
RATIO
V
DE
VALUES IN kΩ.
15:1
5:1
2:1
1:1
1
COMP
1:1
0.1
0.1
0.1
INPUT (dB)
1
gives smaller compression ratios
2:1
8.7
8.7
8.7
COMP
19.4
19.4
19.4
V
5:1
RP
ROT PT
(Pin 10 to GND)
10:1
. For example, a 1
45
45
45
VCA GAIN
15:1
395
N/A
N/A