SSM2165
The SSM2165 Signal Path
operation of the level detector down to 10 Hz, the value of the
capacitor should be around 22 µF. 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.
Figure 11 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 kΩ 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 µF 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 Ω. 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 kΩ impedance between amplifiers determines the
value of this capacitor. For music applications, 10 µF will give
high pass fC = 16 Hz. For voice/communications applications,
1 µF will give fC = 160 Hz. An aluminum electrolytic capacitor
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 Ω, and the external load on Pin 7 should be >5 kΩ. The
nominal output dc voltage of the device is approximately 2.2 V.
Use a dc blocking capacitor for grounded loads.
The rms detector filter time constant is approximately given by
10 × CAVG milliseconds where CAVG is in µF. This time con-
stant controls both the steady-state averaging in the rms detec-
tor 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 fol-
lowed 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 12 for CAVG = 2.2 µF and Figure 13 for CAVG = 22 µF. In
each of these photographs, the input signal to the SSM2165
(not shown) is a series of tone bursts in 6 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 CAVG
but the release times are linear ramps whose decay times are
dependent on both for CAVG and the input signal step size. The
rate of release is approximately 240 dB/s for a CAVG = 2.2 µF,
and 12 dB/s for a CAVG of 22 µF.
,
C2
10F
V+
+
BUF
VCA
IN
OUT
V+
+1
C1
500⍀ 500⍀
0.1F
AUDIO
IN+
V
VCA
OUT
100mV
BUFFER
100
6dBV
90
LEVEL
DETECTOR
CONTROL
SSM2165
AVG CAP
66dBV
+
R1
25k⍀
COMPRESSION
RATIO SET
C3
22F
10
GND
85dBV
0%
100ms
Figure 11. Functional Block Diagram and Typical Voice
Application
Figure 12. RMS Level Detector Performance with
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 Figure 6. 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 Figure 5.
C
AVG = 2.2 µF
1s
100mV
100
90
6dBV
The Level Detector
66dBV
85dBV
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 µF to 22 µF 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
10
0%
Figure 13. RMS Level Detector Performance with
AVG = 22 µF
C
–6–
REV. A
5秒后页面跳转
STM32F030C6芯片介绍：主要参数分析、引脚配置说明、功耗及封装
PCF8591数据手册解读：参数、引脚说明
一文带你了解ss8050参数、引脚配置、应用指南
深入解析AD7606高性能多通道模数转换器：资料手册参数分析
微信公众号
抖音公众号
浙公网安备 33010502006866号 浙ICP备10014259号-119
营业执照ICP证
技术参数
数据手册
如果您发现信息不准确，
