EVALUATION KIT AVAILABLE

MAX9814LE

AVAILABMicrophone Amplifier with AGC and
Low-Noise Microphone Bias
General Description
The MAX9814 is a low-cost, high-quality microphone
amplifier with automatic gain control (AGC) and lownoise microphone bias. The device features a low-noise
preamplifier, variable gain amplifier (VGA), output
amplifier, microphone-bias-voltage generator and AGC
control circuitry.
The low-noise preamplifier has a fixed 12dB gain, while
the VGA gain automatically adjusts from 20dB to 0dB,
depending on the output voltage and the AGC threshold. The output amplifier offers selectable gains of 8dB,
18dB, and 28dB. With no compression, the cascade of
the amplifiers results in an overall gain of 40dB, 50dB,
or 60dB. A trilevel digital input programs the output
amplifier gain. An external resistive divider controls the
AGC threshold and a single capacitor programs theattack/release times. A trilevel digital input programs
the ratio of attack-to-release time. The hold time of the
AGC is fixed at 30ms. The low-noise microphone-biasvoltage generator can bias most electret microphones.
The MAX9814 is available in the space-saving, 14-pin
TDFN package. This device is specified over the-40°C to +85°C extended temperature range.

Applications
Digital Still Cameras
Digital Video Cameras
PDAs
Bluetooth Headsets

Two-Way Communicators

Features♦ Automatic Gain Control (AGC)♦ Three Gain Settings (40dB, 50dB, 60dB)♦ Programmable Attack Time
♦ Programmable Attack and Release Ratio♦ 2.7V to 5.5V Supply Voltage Range♦ Low Input-Referred Noise Density of 30nV/√Hz♦ Low THD: 0.04% (typ)♦ Low-Power Shutdown Mode
♦ Internal Low-Noise Microphone Bias, 2V♦ Available in the Space-Saving, 14-Pin TDFN (3mmx 3mm) Package♦ -40°C to +85°C Extended Temperature Range

Ordering InformationPART

TEMP RANGE

PIN-PACKAGE

MAX9814ETD+T-40°C to +85°C

14 TDFN-EP*+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
*EP = Exposed pad.

High-Quality Portable
Recorders

IP Phones/Telephone
Functional
Diagrams
Conferencing

Pin Configurations appear at end of data sheet.

Entertainment Systems(e.g., Karaoke)

Simplified Block Diagram
2.7V TO 5.5V

SHDN
MICBIAS

LOW-NOISEREFERENCE

VDD

MAX9814AGC

RMICBIAS
CIN

MICIN

LNA
+12dB

Pin Configurations appear at end of data sheet.
Functional Diagrams continued at end of data sheet.
UCSP is a trademark of Maxim Integrated Products, Inc.

VGA
+20dB/0dB

GAIN+8/+18/+28dB

COUT
MICOUT

GND

For pricing, delivery, and ordering information, please contact Maxim Direct
at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.

19-0764; Rev 2; 6/09

MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
ABSOLUTE MAXIMUM RATINGSVDD to GND ..............................................................-0.3V to +6V
All Other Pins to GND.................................-0.3V to (VDD + 0.3V)
Output Short-Circuit Duration.....................................Continuous
Continuous Current (MICOUT, MICBIAS).......................±100mAAll Other Pins ....................................................................±20mA

Continuous Power Dissipation (TA = +70°C)
14-Pin TDFN-EP(derate 16.7mW/°C above +70°C) ........................1481.5mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Lead Temperature (soldering, 10s) .................................+300°C
Bump Temperature (soldering) Reflow............................+235°C

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

ELECTRICAL CHARACTERISTICS(VDD = 3.3V, SHDN = VDD, CCT = 470nF, CCG = 2µF, GAIN = VDD, TA = TMIN to TMAX, unless otherwise specified. Typical values are
at TA = +25°C.) (Note 1)
PARAMETERSYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

GENERAL
Operating Voltage

VDD

5.5

V

Supply Current

IDD

3.1

6

mA

Shutdown Supply Current

ISHDN

0.01

1

µA

Input-Referred Noise Density

BW = 20kHz, all gain settings

30

nV/√HzBW = 20kHz

430

µVRMS

Signal-to-Noise Ratio

BW = 22Hz to 22kHz(500mVRMS output signal)

61

A-weighted

64(Note 2)60

fIN = 1kHz, BW = 20Hz to 20kHz,
RL = 10kΩ, VTH = 1V (threshold = 2VP-P),
VIN = 0.5mVRMS, VCT = 0V

0.04

fIN = 1kHz, BW = 20Hz to 20kHz,
RL = 10kΩ, VTH = 0.1V (threshold =200mVP-P), VIN = 30mVRMS, VCT = 2V

0.2

Total Harmonic Distortion Plus
Noise

Amplifier Input BIAS
Maximum Input Voltage

SNR
DR

THD+N

VIN
VIN_MAX

Input Impedance

ZIN

Maximum Gain

A

Minimum Gain
Maximum Output Level

VOUT_RMS

Regulated Output Level
AGC Attack Time
Attack/Release Ratio

2

2.7

Output Noise

Dynamic Rangeen

Guaranteed by PSRR test

A/R

dB

%

1.14
1% THD

1.23

1.32

mVP-P

100

kΩ

39.5

40

GAIN = GND

49.5

50

50.6

GAIN = unconnected

59.5

60

60.5

GAIN = VDD

18.7

20

20.5

GAIN = GND

29.0

30

30.8

GAIN = unconnected

38.7

40

40.5

1% THD+N, VTH = MICBIAS

40.5

0.707
1.26

V

100

GAIN = VDD

AGC enabled, VTH = 0.7V
tATTACKdB

1.40

CCT = 470nF (Note 3)

1.1

A/R = GND

1:500

A/R = VDD

1:2000A/R = unconnected

1:4000

dB

dB
VRMS

1.54

VP-P
ms
ms/ms

Maxim Integrated

MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
ELECTRICAL CHARACTERISTICS (continued)(VDD = 3.3V, SHDN = VDD, CCT = 470nF, CCG = 2µF, GAIN = VDD, TA = TMIN to TMAX, unless otherwise specified. Typical values are
at TA = +25°C.) (Note 1)
PARAMETERSYMBOLMICOUT High Output Voltage

VOH

IOUT sourcing 1mA

2.45

V

MICOUT Low Output Voltage

VOL

IOUT sinking 1mA

3mV

MICOUT Bias

CONDITIONSMICOUT unconnected

MIN

1.14

TYP

1.23

MAX

1.32

UNITS

V

ZOUT

50

Ω

Minimum Resistive LoadRLOAD_MIN

5kΩMaximum Capacitive Drive

CLOAD_MAX

200

pF

Maximum Output Current

IOUT_MAX

Output Short-Circuit Current

ISC

Output Impedance

1% THD, RL = 500Ω
AGC mode; VDD = 2.7V to 5.5V (Note 4)

Power-Supply Rejection Ratio

PSRR

1
3

8

35

50

f = 217Hz, VRIPPLE = 100mVP-P (Note 5)55

f = 1kHz, VRIPPLE = 100mVP-P (Note 5)

52.5

f = 10kHz, VRIPPLE = 100mVP-P (Note 5)

43

2

mA
mA

dB

MICROPHONE BIAS
Microphone Bias Voltage
Output Resistance
Output Noise Voltage

VMICBIASIMICBIAS = 0.5mA

RMICBIASIMICBIAS = 1mA

VMICBIAS_NOISE IMICBIAS = 0.5mA, BW = 22Hz to 22kHz
DC, VDD = 2.7V to 5.5V

Power-Supply Rejection Ratio

1.84

PSRR

70

IMICBIAS = 0.5mA, VRIPPLE = 100mVP-P,
fIN = 1kHz

2.0

2.18

V

1

Ω

5.5

µVRMS

80
dB

71

TRILEVEL INPUTS (A/R, GAIN)
A/R or GAIN = VDD

0.5VDD 0.5VDD 0.5VDD/ 180kΩ / 100kΩ / 50kΩA/R or GAIN = GND

0.5VDD 0.5VDD 0.5VDD/ 180kΩ / 100kΩ / 50kΩ

Tri-Level Input Leakage Current

mA

Input High Voltage

VIH

Input Low Voltage

VIL

VDD x 0.7

V
VDD x 0.3

V

Shutdown Enable Time

tON

60

ms

Shutdown Disable Time

tOFF

40

ms

DIGITAL INPUT (SHDN)SHDN Input Leakage Current-1

Input High Voltage

VIH

Input Low Voltage

VIL

+1

1.3

µA
V

0.5

V

+1

µA

AGC THRESHOLD INPUT (TH)TH Input Leakage Current-1

Note 1: Devices are production tested at TA = +25°C. Limits over temperature are guaranteed by design.
Note 2: Dynamic range is calculated using the EIAJ method. The input is applied at -60dBFS (0.707µVRMS), fIN = 1kHz.
Note 3: Attack time measured as time from AGC trigger to gain reaching 90% of its final value.
Note 4: CG is connected to an external DC voltage source, and adjusted until VMICOUT = 1.23V.
Note 5: CG connected to GND with 2.2µF.

Maxim Integrated

3

MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
Typical Operating Characteristics(VDD = 5V, CCT = 470nF, CCG = 2.2µF, VTH = VMICBIAS x 0.4, GAIN = VDD (40dB), AGC disabled, no load, RL = 10kΩ, COUT = 1µF,
TA = +25°C, unless otherwise noted.)

-10

-40

-20

-50

50

-30

-60

GAIN = 030

PSRR (dB)

60

40

-40

MAX9814 toc03-30

MAX9814 toc02

GAIN = UNCONNECTED

PSRR (dB)

GAIN (dB)0

MAX9814 toc01

80
70

MICBIAS POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY

POWER-SUPPLY REJECTION RATIO
vs. FREQUENCYGAIN vs. FREQUENCY

-70

-50

-80

20

-60

-90

10

-70

GAIN = 1

0

VRIPPLE = 200mVP-P
-110

-80
100

1k

100k

10k

10

100

1k

10

100k

10k

100

1k

100k

10k

FREQUENCY (Hz)FREQUENCY (Hz)FREQUENCY (Hz)

SUPPLY CURRENT
vs. SUPPLY VOLTAGE

SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE

MICROPHONE BIAS VOLTAGE
vs. MICROPHONE BIAS SOURCE CURRENTSHUTDOWN CURRENT (nA)

3.3
3.2
3.1
3.0
2.9
2.8
2.7

2.5

0.4

2.0
VMICBIAS VOLTAGE (V)

3.4

0.3

0.2

MAX9814 toc06

0.5

MAX9814 toc04

3.5

MAX9814 toc05

10

SUPPLY CURRENT (mA)

-100
VRIPPLE = 200mVP-P

0.1

1.5

1.0

0.5

2.6
0
2.5

3.0

3.5

4.0

4.5

5.0

6.0

5.5

0
2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

5

10

15

20

25

SUPPLY VOLTAGE (V)

IMICBIAS (mA)

TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCYTOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT VOLTAGE

INPUT-REFERRED NOISE
vs. FREQUENCY

1

fIN = 300Hz, 1kHz,
and 3kHzTHD+N (%)

THD+N (%)

1

0.1

0.1

fIN = 10kHz
0.01

0.01
10

100

1k
FREQUENCY (Hz)

10k

100k

30

1000
INPUT-REFERRED NOISE (μVRMS/√Hz)

10

MAX9814 toc08

VOUT = 800mVRMS

MAX9814 toc07

10

4

0

SUPPLY VOLTAGE (V)MICIN AC-COUPLEDTO GND

MAX9814 toc09

2.5

100

10

1
0

0.5

1.0

OUTPUT VOLTAGE (VRMS)

1.5

0.01

0.1

1

10

100

FREQUENCY (kHz)Maxim Integrated

MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
Typical Operating Characteristics (continued)(VDD = 5V, CCT = 470nF, CCG = 2.2µF, VTH = VMICBIAS x 0.4, GAIN = VDD (40dB), AGC disabled, no load, RL = 10kΩ, COUT = 1µF,
TA = +25°C, unless otherwise noted.)

VMICIN
10mV/div
0V

1000

MAX9814 toc12

MAX9814 toc11

MAX9814 toc10

MICBIAS NOISE (nVRMS/√Hz)

TURN-ON RESPONSE

SMALL-SIGNAL PULSE RESPONSE

MICBIAS NOISE vs. FREQUENCY
10,000VSHDN
5V/div
0V

VMICOUT
500mV/div

VMICBIAS
2V/div
0V

0V

VMICOUT
1V/div0V

100

CL = 10pF
10
10

100

1k

10k

100k

20ms/div

200μs/div

FREQUENCY (Hz)

1.00

MAX9814 toc14

MAX9814 toc13

VTH = 1V

VTH = 1V

0.75

VTH = 1V
0.75

0.50
VTH = 0.75V

VOUT (VRMS)

0.75
VOUT (VRMS)

0.50

0.25

0.25

VTH = 0.5V

VTH = 0.5V

VTH = 0.5V

AGC ENABLED
GAIN = 1

0
50

150

100

AGC ENABLED
GAIN = UNCONNECTEDAGC ENABLED
GAIN = 0

0
0

10

20

30

0
0

40

5

15

10

VIN (mVRMS)

VIN (mVRMS)ATTACK TIMEATTACK TIMEHOLD AND RELEASE TIME
MAX9814 toc17

MAX9814 toc16

VIN (mVRMS)

VMICOUT
500mV/div

VMICOUT
500mV/div

0V

0V

VMICOUT
500mV/div0V

CCT = 47nF
200μs/div

Maxim Integrated

VTH = 0.75V

VTH = 0.75V

0.25

0

0.50

MAX9814 toc18

VOUT (VRMS)

VOUT vs. VIN

VOUT vs. VIN
1.00

MAX9814 toc15

VOUT vs. VIN
1.00

CCT = 47nF
A/R = GND

CCT = 100nF
200μs/div

20ms/div

5

MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
Typical Operating Characteristics (continued)(VDD = 5V, CCT = 470nF, CCG = 2.2µF, VTH = VMICBIAS x 0.4, GAIN = VDD (40dB), AGC disabled, no load, RL = 10kΩ, COUT = 1µF,
TA = +25°C, unless otherwise noted.)

HOLD AND RELEASE TIME
MAX9814 toc19

MAX9814 toc20

HOLD AND RELEASE TIME

VMICOUT
500mV/div

VMICOUT
500mV/div

0V

0V
CCT = 47nF
A/R = UNCONNECTED

CCT = 47nF
A/R = VDD

100ms/div

40ms/div

Pin Description
PIN

NAME

FUNCTION

1CT

Timing Capacitor Connection. Connect a capacitor to CT to control the Attack and Release timesof the AGC.

2

SHDN

Active-Low Shutdown Control

3

CG

Amplifier DC Offset Adjust. Connect a 2.2µF capacitor to GND to ensure zero offset at the output.

4, 11

N.C.

No Connection. Connect to GND.

5VDD

Power Supply. Bypass to GND with a 1µF capacitor.

6

MICOUT

7

GND

8

MICIN

Microphone Noninverting Input

A/R

Tri-Level Attack and Release Ratio Select. Controls the ratio of attack time to release time for the
AGC circuit.
A/R = GND: Attack/Release Ratio is 1:500
A/R = VDD: Attack/Release Ratio is 1:2000
A/R = Unconnected: Attack/Release Ratio is 1:4000

GAIN

Tri-Level Amplifier Gain Control.
GAIN = VDD, gain set to 40dB.
GAIN = GND, gain set to 50dB.
GAIN = Unconnected, uncompressed gain set to 60dB.

12

BIAS

Amplifier Bias. Bypass to GND with a 0.47µF capacitor.

13

MICBIAS

TDFN

9

10

6

Amplifier Output
GroundMicrophone Bias Output

14

TH

AGC Threshold Control. TH voltage sets gain control threshold. Connect TH to MICBIAS to disable
the AGC.

—

EP

Exposed Pad. Connect the TDFN EP to GND.

Maxim Integrated

MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
Detailed Description
The MAX9814 is a low-cost, high-quality microphone
amplifier with automatic gain control (AGC) and a lownoise microphone bias. The MAX9814 consists of several distinct circuits: a low-noise preamplifier, a variable
gain amplifier (VGA), an output amplifier, a microphonebias-voltage generator, and AGC control circuitry.
An internal microphone bias voltage generator provides a 2V bias that is suitable for most electret condenser microphones. The MAX9814 amplifies the input
in three distinct stages. In the first stage, the input isbuffered and amplified through the low-noise preamplifier with a gain of 12dB. The second stage consists of
the VGA controlled by the AGC. The VGA/AGC combination is capable of varying the gain from 20dB to 0dB.
The output amplifier is the final stage in which a fixed
gain of 8dB, 18dB, 20dB is programmed through a single tri-level logic input. With no compression from theAGC, the MAX9814 is capable of providing 40dB,
50dB, or 60dB gain.

Automatic Gain Control (AGC)
A device without AGC experiences clipping at the output
when too much gain is applied to the input. AGC prevents clipping at the output when too much gain isapplied to the input, eliminating output clipping. Figure 1
shows a comparison of an over-gained microphone
input with and without AGC.

The MAX9814’s AGC controls the gain by first detecting that the output voltage has exceeded a preset limit.
The microphone amplifier gain is then reduced with aselectable time constant to correct for the excessive
output-voltage amplitude. This process is known as theattack time. When the output signal subsequently lowers in amplitude, the gain is held at the reduced state
for a short period before slowly increasing to the normal value. This process is known as the hold andrelease time. The speed at which the amplifiers adjust
to changing input signals is set by the external timing
capacitor C CT and the voltage applied to A/R. The
AGC threshold can be set by adjusting V TH . Gain
reduction is a function of input signal amplitude with amaximum AGC attenuation of 20dB. Figure 2 shows theeffect of an input burst exceeding the preset limit, output attack, hold and release times.
If the attack and release times are configured torespond too fast, audible artifacts often described as“pumping” or “breathing” can occur as the gain is
rapidly adjusted to follow the dynamics of the signal.
For best results, adjust the time constant of the AGC toaccommodate the source material. For applications inwhich music CDs are the main audio source, a 160µs
attack time with an 80ms release time is recommended. Music applications typically require a shorterrelease time than voice or movie content.

MAX9814 AGC DISABLED

MAX9814 AGC ENABLED

MAX9814 fig01a

MAX9814 fig01b

0V

VMICIN
100mV/div

0V

0V

VMICOUT(AC-COUPLED)
1V/div0V

400μs/div

VMICIN
100mV/div

VMICOUT(AC-COUPLED)
1V/div

400μs/div

Figure 1. Microphone Input with and Without AGC

Maxim Integrated

7

MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Biasand setting the attack-to-release time ratio by configuring A/R as shown in Table 1:
HOLD
VCT
500mV/div
ATTACK• Use a small ratio to maximize the speed of the AGC.
• Use a large ratio to maximize the sound quality andprevent repeated excursions above the thresholdfrom being independently adjusted by the AGC.

RELEASE

0V
VMICOUT(AC-COUPLED)
1V/div0V

AGC Output Threshold
The output threshold that activates AGC is adjustablethrough the use of an external resistive divider. Oncethe divider is set, AGC reduces the gain to match theoutput voltage to the voltage set at the TH input.

Microphone Bias
10ms/div

Figure 2. Input Burst Exceeding AGC Limit

Attack TimeThe attack time is the time it takes for the AGC to
reduce the gain after the input signal has exceeded thethreshold level. The gain attenuation during the attack
time is exponential, and defined as one-time constant.
The time constant of the attack is given by 2400 x CCT
seconds (where CCT is the external timing capacitor):• Use a short attack time for the AGC to react quickly
to transient signals, such as snare drum beats(music) or gun shots (DVD).
• Use a longer attack time to allow the AGC to ignore
short-duration peaks and only reduce the gain whena noticeable increase in loudness occurs. Shortduration peaks are not reduced, but louder passages are. This allows the louder passages to be
reduced in volume, thereby maximizing output
dynamic range.
Hold Time
Hold time is the delay after the signal falls below thethreshold level before the release phase is initiated.
Hold time is internally set to 30ms and nonadjustable.
The hold time is cancelled by any signal exceeding theset threshold level, and the attack time is reinitiated.
Release TimeThe release time is how long it takes for the gain to
return to its normal level after the output signal has fallen below the threshold level and 30ms hold time has
expired. Release time is defined as release from a
20dB gain compression to 10% of the nominal gain setting after the input signal has fallen below the TH
threshold and the 30ms hold time has expired. Releasetime is adjustable and has a minimum of 25ms. The
release time is set by picking an attack time using CCT
8The MAX9814 features an internal low-noise microphone bias voltage capable of driving most electretcondenser microphones. The microphone bias is regulated at 2V to provide that the input signal to the lownoise preamplifier does not clip to ground.

Applications Information
Programming Attack and Release Times
Attack and release times are set by selecting thecapacitance value between CT and GND, and by setting the logic state of A/R (Table 1). A/R is a tri-level
logic input that sets the attack-to-release time ratio.

Table 1. Attack-and-Release Ratios
A/R

ATTACK/RELEASE RATIO

GND

1:500

VDD

1:2000Unconnected

1:4000

The attack and release times can be selected by utilizing the corresponding capacitances listed in Table 2.

Table 2. Attack-and-Release Time
CCT

tATTACK(ms)

22nF

tRELEASE (ms)
A/R =
GND

A/R =
VDD

A/R =
UNCONNECTED

0.05

25

100

200

47nF

0.11

55

220

440

68nF

0.16

80

320

640

100nF

0.24

120

480

960

220nF

0.53

265

1060

2120

470nF

1.1

550

2200

4400

680nF

1.63

815

3260

6520

1µF

2.4

1200

4800

9600

Maxim Integrated

MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
Setting the AGC Threshold
To set the output-voltage threshold at which the microphone output is clamped, an external resistor-divider
must be connected from MICBIAS to ground with the output of the resistor-divider applied to TH. The voltage VTH
determines the peak output-voltage threshold at which
the output becomes clamped. The maximum signal
swing at the output is then limited to two times VTH andremains at that level until the amplitude of the input signal
is reduced. To disable AGC, connect TH to MICBIAS.

Microphone Bias Resistor
MICBIAS is capable of sourcing 20mA. Select a value for
RMICBIAS that provides the desired bias current for theelectret microphone. A value of 2.2kΩ is usually sufficient
for a microphone of typical sensitivity. Consult the microphone data sheet for the recommended bias resistor.

Bias Capacitor
The BIAS output of the MAX9814 is internally bufferedand provides a low-noise bias. Bypass BIAS with a
470nF capacitor to ground.

Input Capacitor
The input AC-coupling capacitor (CIN) and the input
resistance (RIN) to the microphone amplifier form ahighpass filter that removes any DC bias from an input
signal (see the Typical Application Circuit/Functional
Diagram). CIN prevents any DC components from the
input-signal source from appearing at the amplifier outputs. The -3dB point of the highpass filter, assuming
zero source impedance due to the input signal source,
is given by:
f−3dB_IN =Maxim Integrated

12π × RIN × CIN

Choose CIN such that f-3dB_IN is well below the lowest
frequency of interest. Setting f-3dB_IN too high affects theamplifier’s low-frequency response. Use capacitors withlow-voltage coefficient dielectrics. Aluminum electrolytic,
tantalum, or film dielectric capacitors are good choices
for AC-coupling capacitors. Capacitors with high-voltage
coefficients, such as ceramics (non-C0G dielectrics), canresult in increased distortion at low frequencies.

Output Capacitor
The output of the MAX9814 is biased at 1.23V. To eliminate the DC offset, an AC-coupling capacitor (COUT)
must be used. Depending on the input resistance (RL)of the following stage, COUT and RL effectively form ahighpass filter. The -3dB point of the highpass filter,
assuming zero output impedance, is given by:
f−3dB_OUT =1
2π × RL × COUT

Shutdown
The MAX9814 features a low-power shutdown mode.
When SHDN goes low, the supply current drops to
0.01µA, the output enters a high-impedance state, andthe bias current to the microphone is switched off.
Driving SHDN high enables the amplifier. Do not leave
SHDN unconnected.

Power-Supply Bypassing
and PCB Layout
Bypass the power supply with a 0.1µF capacitor to
ground. Reduce stray capacitance by minimizing trace
lengths and place external components as close to thedevice as possible. Surface-mount components arerecommended. In systems where analog and digital
grounds are available, connect the MAX9814 to analog
ground.

9

MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
Typical Application Circuit/Functional Diagram
VDD

CBYPASS
1μF

SHDN

VDD
MICBIAS

MAX9814
BIAS

A/R

CBIAS
0.47μF

R1
150kΩ

TH
VDD

MICBIAS

REF

AGC
GAIN

R2
100kΩ

RMICBIAS
2.21kΩ
MICIN

LNA

VGA

CIN
0.1μF

MICOUT

COUT

ROUT
CT
CCT
470nF
CG
CCG
2.2μF
GND

*THE DEVICE HAS BEEN CONFIGURED WITH AN ATTACK TIME OF 1.1ms, 40dB GAIN, AND AN ATTACK-AND-RELEASE RATIO OF 1:500.

10

Maxim Integrated

MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
Pin Configuration

Chip Information
PROCESS: BiCMOSTHMICBIAS

BIAS

N.C.

GAIN

A/R

MICIN

TOP VIEW

14

13

12

11

10

9

8

MAX9814

5

6

7
GND

CG

4

MICOUT

3

VDD

2

N.C.

1

SHDN

*EP

CT

+

TDFN

Maxim Integrated

11

MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages.

12

PACKAGE TYPE

PACKAGE CODE

DOCUMENT NO.

14 TDFN-EP

T1433-2

21-0137

Maxim Integrated

MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
Package Information (continued)
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages.

COMMON DIMENSIONSPACKAGE VARIATIONSSYMBOL

MIN.

MAX.

PKG. CODE

N

D2

E2

e

JEDEC SPEC

b

A

0.70

0.80

T633-26

1.50±0.10

2.30±0.10

0.95 BSC

MO229 / WEEA

0.40±0.05

1.90 REF

D

2.90

3.10

T833-281.50±0.10

2.30±0.10

0.65 BSC

MO229 / WEEC

0.30±0.05

1.95 REF[(N/2)-1] x e

E

2.90

3.10

T833-381.50±0.10

2.30±0.10

0.65 BSC

MO229 / WEEC

0.30±0.05

1.95 REF

A1

0.00

0.05

T1033-110

1.50±0.10

2.30±0.10

0.50 BSC

MO229 / WEED-3

0.25±0.05

2.00 REF

L

0.20

0.40

T1033MK-1101.50±0.10

2.30±0.10

0.50 BSC

MO229 / WEED-3

0.25±0.05

2.00 REF

k

0.25 MIN.

T1033-2101.50±0.10

2.30±0.10

0.50 BSC

MO229 / WEED-3

0.25±0.05

2.00 REF

A2

0.20 REF.

T1433-114

1.70±0.10

2.30±0.10

0.40 BSC----

0.20±0.05

2.40 REF

T1433-214

1.70±0.10

2.30±0.10

0.40 BSC----

0.20±0.05

2.40 REF

T1433-3F

14

1.70±0.10

2.30±0.10

0.40 BSC----

0.20±0.05

2.40 REF

Maxim Integrated

13

MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
Revision History
REVISIONNUMBERREVISION
DATE

0

3/07

Initial release

1

2/09

Updated Ordering Information, Absolute Maximum Ratings, Pin Description, and Pin
Configuration sections to include EP for TDFN package

2

6/09

Removed UCSP package

DESCRIPTIONPAGESCHANGED—1, 2, 6, 11
1, 2, 6, 11, 12

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.
Maxim reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical
Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.

14©

Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000
Maxim Integrated

The Maxim logo and Maxim Integrated are trademarks of Maxim Integrated Products, Inc.