Analog Devices SSM2165-2S, SSM2165-1S, SSM2165-1P Datasheet

a Microphone Preamplifier with

Variable Compression and Noise Gating

SSM2165*

FEATURES

Complete Microphone Conditioner in an 8-Lead Package Single 5 V Operation

Preset Noise Gate Threshold

Compression Ratio Set by External Resistor Automatic Limiting Feature Prevents ADC Overload Adjustable Release Time

Low Noise and Distortion

20 kHz Bandwidth ( 1 dB)

Low Cost

APPLICATIONS

Microphone Preamplifier/Processor

Computer Sound Cards

Public Address/Paging Systems

Communication Headsets

Telephone Conferencing

Guitar Sustain Effects Generator

Computerized Voice Recognition

Surveillance Systems

Karaoke and DJ Mixers

GENERAL DESCRIPTION

The SSM2165 is a complete and flexible solution for conditioning microphone inputs in computer audio systems. It is also excellent for improving vocal clarity in communications and public address systems. A low noise voltage controlled amplifier (VCA) provides a gain that is dynamically adjusted by a control loop to maintain a set compression characteristic. The compression ratio is set by a single resistor and can be varied from 1:1 to over 15:1 relative to the fixed rotation point. Signals above the rotation point are limited to prevent overload and to eliminate “popping.” A downward expander (noise gate) prevents amplification of noise or hum. This results in optimized signal levels prior to digitization, thereby eliminating the need for additional gain or attenuation in the digital domain that could add noise or impair accuracy of speech recognition algorithms. The flexibility of setting the compression ratio and the time constant of the level detector, coupled with two values of rotation point, make the SSM2165 easy to integrate in a wide variety of microphone conditioning applications.

The SSM2165 is an ideal companion product for audio codecs used in computer systems, such as the AD1845 and AD1847. The device is available in 8-lead SOIC and P-DIP packages, and guaranteed for operation over the extended industrial temperature range of –40° C to +85° C. As shown in Figure 1a, the SSM2165-1 has a rotation point of –25.7 dBu (40 mV)1, a VCA gain of 18 dB, and gives –7.7 dBu (320 mV) before limiting. As shown in Figure 1b, the SSM2165-2 has a rotation point of –17.8 dBu (100 mV),

*Patents pending.

1All signals are in rms volts or dBu (0 dBu = 0.775 V rms).

REV. B

Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

		FUNCTIONAL BLOCK DIAGRAM
			C2
		V+	10 F
			+
	C1	V+	BUFOUT	VCAIN
			RA	RA
AUDIO	0.1 F		2	2
		+1			VCA	VOUT
IN+
		BUFFER
			LEVEL		CONTROL
			DETECTOR
		SSM2165
			AVG CAP	+	R1	COMPRESSION
			C3
		GND	22 F		25k	RATIO SET

a VCA gain of 8 dB and gives –9.8 dBu (250 mV) before limiting. Both have a noise gate threshold of –64 dBu (500 V), below which downward expansion reduces the gain with a ratio of approximately 1:3. That is, a –3 dB reduction of output signal occurs with a –1 dB reduction of input signal. For applications requiring adjustable noise gate threshold, VCA gain up to 18 dB, and adjustable rotation point, please refer to the SSM2166.

	0
	–10
– dBu	–20
	–30
OUTPUT
	–40
	–50
	–60
	–80	–70	–60	–50	–40	–30	–20	–10

INPUT – dBu

Figure 1a. SSM2165-1 Compression and Gating Characteristics

	0
	–10
dBu	–20
	–30
–
OUTPUT	–40
	–50
	–60
	–70	–70	–60	–50	–40	–30	–20	–10
	–80

INPUT – dBu

Figure 1b. SSM2165-2 Compression and Gating Characteristics

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: [phone]	www.analog.com
Fax: [phone]	© Analog Devices, Inc., 2002

SSM2165–SPECIFICATIONS (V+ = 5 V, f = 1 kHz, RL = 100 k , RCOMP = 0 , TA = 25 C, unless otherwise noted)

Parameter	Symbol	Conditions	Min Typ	Max	Unit
AUDIO SIGNAL PATH	en				nV/√ Hz2
Voltage Noise Density		15:1 Compression, VIN = GND	17
Noise		20 kHz Bandwidth, VIN = GND	–109		dBu1
Total Harmonic Distortion	THD+N
SSM2165-1		2nd and 3rd Harmonics, VIN = –30 dBu	0.2	0.5	%
SSM2165-2		2nd and 3rd Harmonics, VIN = –20 dBu	0.2	0.5	%
		22 kHz Low-Pass Filter			kΩ
Input Impedance	ZIN		180
Output Impedance	ZOUT		75		Ω
Load Drive		Resistive	5		kΩ
		Capacitive		2	nF
Input Voltage Range		1% THD	1		V rms
Output Voltage Range		1% THD	1.4		V rms
Gain Bandwidth Product		1:1 Compression
SSM2165-1		VCA G = 18 dB	300		kHz
SSM2165-2		VCA G = 8 dB	100		kHz
CONTROL SECTION
VCA Dynamic Gain Range			40		dB
VCA Fixed Gain
SSM2165-1			18		dB
SSM2165-2			8		dB
Rotation Point
SSM2165-1			40		mV rms
SSM2165-2			100		mV rms
Compression Ratio, Min			1:1
Compression Ratio, Max			15:1
Control Feedthrough		15:1 Compression	± 5		mV
POWER SUPPLY
Supply Voltage Range	VS		4.5	5.5	V
Supply Current	ISY		7.5	10	mA
Quiescent Output Voltage Level			2.2		V
Power Supply Rejection Ratio2	PSRR		50		dB

NOTES

10 dBu = 0.775 V rms.

2Referred to input.

Specifications subject to change without notice.

–2–

REV. B

SSM2165

ABSOLUTE MAXIMUM RATINGS
Supply Voltage .		. . . . . . . . . . . . . . .	.	. . . . . . . . . . . . .	. . . . 10 V
Audio Input Voltage . . . . . . . . . . . .				. . . . . . . . . Supply Voltage
Operating Temperature Range . . . .				. . . . . . . . –40° C to +85° C
Storage Temperature Range . . . . . .				. . . . . . . –65° C to +150° C
Junction Temperature (TJ) . . . . . . .				. . . . . . . . . . . . .	. . . 150° C
Lead Temperature (Soldering, 60 sec) . . . . . . . . . . .					. . . 300° C
ESD RATINGS
883 (Human Body) Model . . . . . . .				. . . . . . . . . . . . .	. . . 2.0 kV
THERMAL CHARACTERISTICS
Thermal Resistance
8-Lead Plastic DIP					103° C/W
θ JA . . . . . .		. . . . . . . . . . . . . . .	.	. . . . . . . . . . . . .
θ JC . . . . . .		. . . . . . . . . . . . . . .	.	. . . . . . . . . . . . .	. 43° C/W
8-Lead SOIC					158° C/W
θ JA . . . . . .		. . . . . . . . . . . . . . .	.	. . . . . . . . . . . . .
θ JC . . . . . .		. . . . . . . . . . . . . . .	.	. . . . . . . . . . . . .	. 43° C/W
		ORDERING GUIDE
		Temperature		Package	Package
Model		Range		Description	Options
SSM2165-1P*		–40° C to +85° C		Plastic DIP	N-8
SSM2165-1S		–40° C to +85° C		Narrow SOIC	SO-8
SSM2165-2S		–40° C to +85° C		Narrow SOIC	SO-8

*Not for new design, obsolete April 2002.

PIN CONFIGURATION

	GND	1				8	V+
			SSM2165
	VCAIN	2				7	OUTPUT
			TOP VIEW
	BUFOUT	3				6	COMP RATIO SET
			(Not to Scale)
	AUDIO +IN	4				5	AVG CAP

PIN FUNCTION DESCRIPTIONS

Pin #	Mnemonic	Function
1	GND	Ground
2	VCAIN	VCA Input Pin. A typical
		connection is a 1 µ F–10 µ F
		capacitor from the buffer output
		pin (Pin 3) to this pin.
3	BUFOUT	Input Buffer Amplifier Output
		Pin. Must not be loaded by
		capacitance to ground.
4	AUDIO +IN	Input Audio Signal. The input
		signal should be ac-coupled
		(0.1 µ F typical) into this pin.
5	AVG CAP	Detector Averaging Capacitor.
		A capacitor, 2.2 µ F–22 µ F, to
		ground from this pin is the
		averaging capacitor for the
		detector circuit.
6	COMP RATIO SET	Compression Ratio Set Pin. A
		resistor to ground from this pin
		sets the compression ratio as
		shown in TPC 1.
7	OUTPUT	Output Signal.
8	V+	Positive Supply, 5 V Nominal.

CAUTION

ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the SSM2165 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high-energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.

WARNING!

ESD SENSITIVE DEVICE

REV. B

–3–

SSM2165–Typical Performance Characteristics

	260
	240	TA 25 C
	220	VS 5V
		RL 100k
	200
	180
k	160
	140
–
COMP
	120
R	100		SSM2165–1
	80
	60			SSM2165–2
	40
	20
	0
	1:1	2:1	5:1	10:1	15:1

COMPRESSION RATIO

TPC 1. Compression Ratio vs. RCOMP

	5
	TA 25 C
	COMP RATIO 1:1
	RL 100k /10k
	VS 5V
THD N – %	1
			SSM2165–1
	0.1		SSM2165–2
0.050		0.1
	0.01		1

INPUT – V rms

TPC 2. THD + N (%) vs. Input (V rms)

5	TA 25 C
	VS 5V
	COMP RATIO 1:1
	VI N –20dBu (–1)
	VI N –30dBu (–2)
1	RL 100k
THD N – %
	SSM2165–1
0.1
	SSM2165–2
0.050	100	1k	10k	30k
20

FREQUENCY – Hz

TPC 3. THD + N (%) vs. Frequency (Hz)

	5 V	1s
100
90
10	TA 25 C
0%	COMPRESSION RATIO 15:1
	NOISE BW 20kHz

		TPC 4. Wideband Output Noise
	70
	60		COMP RATIO 15:1
			RCOMP 0
	50		VIN 40 V rms
	40
dB	30
–
GAIN	20	G = 18dB
	10	G = 8dB
	0
	–10
	–20	10k	100k	1M
	1k
			FREQUENCY – Hz

TPC 5. GBW Curves vs. VCA Gain

–30

	–40
– dB	–50		V+ 5 1V p-p
PSRR
	–60
	–70
	20	100	1k	10k	30k
			FREQUENCY – Hz

TPC 6. PSRR vs. Frequency, Referred to Input

–4–

REV. B