SSM2165-1S-REEL7 Analog Devices Inc, SSM2165-1S-REEL7 Datasheet - Page 6

• Manufacturer Part Number: SSM2165-1S-REEL7
• Description: IC PREAMP AUDIO MONO AB 8SOIC
• Manufacturer: Analog Devices Inc
• Type: Class ABr

Specifications of SSM2165-1S-REEL7

• 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: 8-SOIC (3.9mm Width)
• Max Output Power X Channels @ Load: -

SSM2165
The SSM2165 Signal Path
Figure 3 illustrates the block diagram of the SSM2165. The
audio input signal is processed by the unity gain input buffer
and then by the VCA. The buffer presents an input impedance
of approximately 180 k to the source. A dc voltage of approxi-
mately 1.5 V is present at AUDIO +IN (Pin 4), requiring the
use of a blocking capacitor (C1) for ground-referenced sources.
A 0.1 F capacitor is a good choice for most audio applications.
The buffer is designed to drive only the low impedance input of
the VCA, and must not be loaded by capacitance to ground.
The VCA is a low distortion, variable-gain amplifier whose gain
is set by the internal control circuitry. The input to the VCA is
a virtual ground in series with 500 . An external blocking
capacitor (C2) must be used between the buffer’s output and
the VCA input. The desired low frequency response and the
total of 1 k
value of this capacitor. For music applications, 10 F will give
high pass f
1 F will give f
is an economical choice. The VCA amplifies the input signal
current flowing through C6 and converts this current to a
voltage at the SSM2165’s output (Pin 7). The net gain from
input to output can be as high as 40 dB for high compression
ratios and depending on the gain set by the control circuitry.
The output impedance of the SSM2165 is typically less than
75 , and the external load on Pin 7 should be >5 k . The
nominal output dc voltage of the device is approximately 2.2 V.
Use a dc blocking capacitor for grounded loads.
The bandwidth of the SSM2165 is quite wide at all gain set-
tings. The upper –3 dB point is approximately 300 kHz. The
GBW plots are shown in TPC 5. While the noise of the input
buffer is fixed, the input referred noise of the VCA is a function
of gain. The VCA input noise is designed to be a minimum
when the gain is at a maximum, thereby optimizing the usable
dynamic range of the part. A photograph of the SSM2165’s
wideband peak-to-peak output noise is illustrated in TPC 4.
The Level Detector
The SSM2165 incorporates a full-wave rectifier and a patent-
pending, true rms level detector circuit whose averaging time
constant is set by an external capacitor connected to the AVG
CAP pin (Pin 5). Capacitor values from 18 F to 22 F have
been found to be more appropriate in voiceband applications,
where capacitors on the low end of the range seem more appro-
priate for music program material. For optimal low frequency
AUDIO
IN+
0.1 F
C
C1
= 16 Hz. For voice/communications applications,
impedance between amplifiers determine the
C
SSM2165
= 160 Hz. An aluminum electrolytic capacitor
GND
V+
+1
V+
BUFFER
BUF
LEVEL
DETECTOR
500
OUT
AVG CAP
10 F
500
22 F
C2
C3
+
VCA
+
25k
IN
CONTROL
R1
VCA
COMPRESSION
RATIO SET
V
OUT
operation of the level detector down to 10 Hz, the value of the
capacitor should be around 22 F. Some experimentation with
larger values for the AVG CAP may be necessary to reduce the
effects of excessive low frequency ambient background noise.
The value of the averaging capacitor affects sound quality: too
small a value for this capacitor may cause a “pumping effect”
for some signals, while too large a value can result in slow re-
sponse times to signal dynamics. Electrolytic capacitors are
recommended here for lowest cost.
The rms detector filter time constant is approximately given by
10
stant controls both the steady-state averaging in the rms
detector as well as the release time for compression, that is, the
time it takes for the system gain to react when a large input is
followed by a small signal. The attack time, the time it takes for
the gain to be reduced when a small signal is followed by a large
signal, is mainly controlled by internal circuitry that speeds up
the attack for large level changes, and controlled partly by the
AVG CAP value. This limits overload time to under 1 ms in
most cases.
The performance of the rms level detector is illustrated in Fig-
ure 4 for C
of these photographs, the input signal to the SSM2165 (not
shown) is a series of tone bursts in six successive 10 dB steps.
The tone bursts range from –66 dBu (0.5 mV rms) to
–6 dBu (0.5 V rms). As illustrated in the photographs, the
attack time of the rms level detector is dependent only on C
but the release times are linear ramps whose decay times are
dependent on both for C
rate of release is approximately 240 dB/s for a C
and 12 dB/s for a C
C
AVG
100
100
0%
0%
90
10
90
10
AVG
milliseconds where C
= 2.2 F and Figure 5 for C
100mV
100mV
AVG
of 22 F.
AVG
and the input signal step size. The
AVG
100ms
is in F. This time con-
1s
AVG
= 22 F. In each
AVG
6dBV
66dBV
85dBV
6dBV
66dBV
85dBV
= 2.2 F,
AVG
,