AVAILABLE
EVALUATION KIT AVAILABLE
Functional Diagrams
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.
For pricing, delivery, and ordering information, please contact Maxim Direct
at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.
General Description
The MAX9814 is a low-cost, high-quality microphone
amplifier with automatic gain control (AGC) and low-
noise 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 thresh-
old. 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 the
attack/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-bias-
voltage 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
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 (3mm
x 3mm) Package
♦-40°C to +85°C Extended Temperature Range
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
Ordering Information
Simplified Block Diagram
LOW-NOISE
REFERENCE AGC
2.7V TO 5.5V
LNA
+12dB
VGA
+20dB/0dB
GAIN
+8/+18/
+28dB
MICBIAS
RMICBIAS
MICIN MICOUT
COUT
GND
CIN
VDD
SHDN
MAX9814
PART 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.
Pin Configurations appear at end of data sheet.
Digital Still Cameras
Digital Video Cameras
PDAs
Bluetooth Headsets
Entertainment Systems
(e.g., Karaoke)
Two-Way Communicators
High-Quality Portable
Recorders
IP Phones/Telephone
Conferencing
MAX9814
19-0764; Rev 2; 6/09
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
ABSOLUTE MAXIMUM RATINGS
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)
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.
VDD 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).......................±100mA
All 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
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
GENERAL
Operating Voltage VDD Guaranteed by PSRR test 2.7 5.5 V
Supply Current IDD 3.1 6 mA
Shutdown Supply Current ISHDN 0.01 1 µA
Input-Referred Noise Density enBW = 20kHz, all gain settings 30 nV/√Hz
Output Noise BW = 20kHz 430 µVRMS
BW = 22Hz to 22kHz
(500mVRMS output signal) 61
Signal-to-Noise Ratio SNR
A-weighted 64
dB
Dynamic Range DR (Note 2) 60 dB
fIN = 1kHz, BW = 20Hz to 20kHz,
RL
= 10kΩ , V
T H
= 1V ( thr eshol d = 2V
P - P
) ,
V
I N = 0.5m V
R M S
, V
C T = 0V
0.04
Total Harmonic Distortion Plus
Noise THD+N fIN = 1kHz, BW = 20Hz to 20kHz,
RL = 10kΩ, VTH = 0.1V (threshold =
200mVP-P), VIN = 30mVRMS, VCT = 2V
0.2
%
Amplifier Input BIAS VIN 1.14 1.23 1.32 V
Maximum Input Voltage VIN_MAX 1% THD 100 mVP-P
Input Impedance ZIN 100 kΩ
GAIN = VDD 39.5 40 40.5
GAIN = GND 49.5 50 50.6
Maximum Gain A
GAIN = unconnected 59.5 60 60.5
dB
GAIN = VDD 18.7 20 20.5
GAIN = GND 29.0 30 30.8Minimum Gain
GAIN = unconnected 38.7 40 40.5
dB
Maximum Output Level VOUT_RMS 1% THD+N, VTH = MICBIAS 0.707 VRMS
Regulated Output Level AGC enabled, VTH = 0.7V 1.26 1.40 1.54 VP-P
AGC Attack Time tATTACK CCT = 470nF (Note 3) 1.1 ms
A/R = GND 1:500
A/R = VDD 1:2000
Attack/Release Ratio A/R
A/R = unconnected 1:4000
ms/ms
MAX9814
2
Maxim Integrated
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
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.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
MICOUT High Output Voltage VOH IOUT sourcing 1mA 2.45 V
MICOUT Low Output Voltage VOL IOUT sinking 1mA 3 mV
MICOUT Bias MICOUT unconnected 1.14 1.23 1.32 V
Output Impedance ZOUT 50 Ω
Minimum Resistive Load RLOAD_MIN 5kΩ
Maximum Capacitive Drive CLOAD_MAX 200 pF
Maximum Output Current IOUT_MAX 1% THD, RL = 500Ω12mA
Output Short-Circuit Current ISC 38 mA
AGC mode; VDD = 2.7V to 5.5V (Note 4) 35 50
f = 217Hz, VRIPPLE = 100mVP-P (Note 5) 55
f = 1kHz, VRIPPLE = 100mVP-P (Note 5) 52.5
Power-Supply Rejection Ratio PSRR
f = 10kHz, VRIPPLE = 100mVP-P (Note 5) 43
dB
MICROPHONE BIAS
Microphone Bias Voltage VMICBIAS IMICBIAS = 0.5mA 1.84 2.0 2.18 V
Output Resistance RMICBIAS IMICBIAS = 1mA 1 Ω
Output Noise Voltage VMICBIAS_NOISE IMICBIAS = 0.5mA, BW = 22Hz to 22kHz 5.5 µVRMS
DC, VDD = 2.7V to 5.5V 70 80
Power-Supply Rejection Ratio PSRR IMICBIAS = 0.5mA, VRIPPLE = 100mVP-P,
fIN = 1kHz 71 dB
TRILEVEL INPUTS (A/R, GAIN)
A/R or GAIN = VDD 0.5VDD
/ 180kΩ
0.5VDD
/ 100kΩ
0.5VDD
/ 50kΩ
Tri-Level Input Leakage Current
A/R or GAIN = GND 0.5VDD
/ 180kΩ
0.5VDD
/ 100kΩ
0.5VDD
/ 50kΩ
mA
Input High Voltage VIH VDD x 0.7 V
Input Low Voltage VIL 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 +1 µA
Input High Voltage VIH 1.3 V
Input Low Voltage VIL 0.5 V
AGC THRESHOLD INPUT (TH)
TH Input Leakage Current -1 +1 µA
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)
MAX9814
Maxim Integrated
3
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.)
GAIN vs. FREQUENCY
MAX9814 toc01
FREQUENCY (Hz)
GAIN (dB)
10k1k100
10
20
30
40
50
60
70
80
0
10 100k
GAIN = UNCONNECTED
GAIN = 0
GAIN = 1
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX9814 toc02
FREQUENCY (Hz)
PSRR (dB)
10k1k100
-70
-60
-50
-40
-30
-20
-10
0
-80
10 100k
VRIPPLE = 200mVP-P
MICBIAS POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX9814 toc03
FREQUENCY (Hz)
PSRR (dB)
10k1k100
-100
-90
-80
-70
-60
-50
-40
-30
-110
10 100k
VRIPPLE = 200mVP-P
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX9814 toc04
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
5.55.04.0 4.53.53.0
2.6
2.7
2.8
2.9
3.0
3.1
3.2
3.3
3.4
3.5
2.5
2.5 6.0
SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE
MAX9814 toc05
SUPPLY VOLTAGE (V)
SHUTDOWN CURRENT (nA)
5.55.04.54.03.53.0
0.1
0.2
0.3
0.4
0.5
0
2.5 6.0
MICROPHONE BIAS VOLTAGE
vs. MICROPHONE BIAS SOURCE CURRENT
MAX9814 toc06
IMICBIAS (mA)
VMICBIAS VOLTAGE (V)
252015105
0.5
1.0
1.5
2.0
2.5
0
030
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
MAX9814 toc07
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.1
1
10
0.01
10 100k
VOUT = 800mVRMS
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT VOLTAGE
MAX9814 toc08
OUTPUT VOLTAGE (VRMS)
THD+N (%)
1.0
0.5
0.1
1
10
0.01
0 1.5
fIN = 300Hz, 1kHz,
and 3kHz
fIN = 10kHz
INPUT-REFERRED NOISE
vs. FREQUENCY
MAX9814 toc09
FREQUENCY (kHz)
INPUT-REFERRED NOISE (μVRMS/√Hz)
1010.1
100
10
0.01 100
1000
1
MICIN AC-COUPLED
TO GND
MAX9814
4
Maxim Integrated
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
MICBIAS NOISE vs. FREQUENCY
MAX9814 toc10
FREQUENCY (Hz)
MICBIAS NOISE (nVRMS/√Hz)
10k1k100
100
1000
10,000
10
10 100k
SMALL-SIGNAL PULSE RESPONSE
MAX9814 toc11
200μs/div
VMICIN
10mV/div
0V
VMICOUT
500mV/div
0V
CL = 10pF
TURN-ON RESPONSE
MAX9814 toc12
20ms/div
VSHDN
5V/div
0V
VMICBIAS
2V/div
0V
VMICOUT
1V/div
0V
VOUT vs. VIN
MAX9814 toc13
VIN (mVRMS)
VOUT (VRMS)
10050
0.25
0.50
0.75
1.00
0
0 150
VTH = 1V
VTH = 0.75V
VTH = 0.5V AGC ENABLED
GAIN = 1
VOUT vs. VIN
MAX9814 toc14
VIN (mVRMS)
VOUT (VRMS)
302010
0.25
0.50
0.75
1.00
0
040
VTH = 1V
VTH = 0.75V
VTH = 0.5V
AGC ENABLED
GAIN = 0
VOUT vs. VIN
MAX9814 toc15
VIN (mVRMS)
VOUT (VRMS)
105
0.25
0.50
0.75
1.00
0
015
VTH = 1V
VTH = 0.75V
VTH = 0.5V
AGC ENABLED
GAIN = UNCONNECTED
ATTACK TIME
MAX9814 toc16
200μs/div
VMICOUT
500mV/div
CCT = 47nF
0V
ATTACK TIME
MAX9814 toc17
200μs/div
VMICOUT
500mV/div
CCT = 100nF
0V
HOLD AND RELEASE TIME
MAX9814 toc18
20ms/div
VMICOUT
500mV/div
CCT = 47nF
A/R = GND
0V
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.)
MAX9814
Maxim Integrated
5
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
HOLD AND RELEASE TIME
MAX9814 toc19
40ms/div
VMICOUT
500mV/div
CCT = 47nF
A/R = VDD
0V
HOLD AND RELEASE TIME
MAX9814 toc20
100ms/div
VMICOUT
500mV/div
CCT = 47nF
A/R = UNCONNECTED
0V
Pin Description
PIN
TDFN
NAME FUNCTION
1CT
Timing Capacitor Connection. Connect a capacitor to CT to control the Attack and Release times
of the AGC.
2SHDN 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.
5V
DD Power Supply. Bypass to GND with a 1µF capacitor.
6 MICOUT Amplifier Output
7 GND Ground
8 MICIN Microphone Noninverting Input
9A/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
10 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 Microphone 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.
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.)
MAX9814
6
Maxim Integrated
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
MAX9814 AGC DISABLED
400μs/div
VMICIN
100mV/div
VMICOUT
(AC-COUPLED)
1V/div
MAX9814 fig01a
MAX9814 AGC ENABLED
400μs/div
VMICIN
100mV/div
VMICOUT
(AC-COUPLED)
1V/div
MAX9814 fig01b
0V
0V
0V
0V
Detailed Description
The MAX9814 is a low-cost, high-quality microphone
amplifier with automatic gain control (AGC) and a low-
noise microphone bias. The MAX9814 consists of sever-
al distinct circuits: a low-noise preamplifier, a variable
gain amplifier (VGA), an output amplifier, a microphone-
bias-voltage generator, and AGC control circuitry.
An internal microphone bias voltage generator pro-
vides a 2V bias that is suitable for most electret con-
denser microphones. The MAX9814 amplifies the input
in three distinct stages. In the first stage, the input is
buffered and amplified through the low-noise preampli-
fier with a gain of 12dB. The second stage consists of
the VGA controlled by the AGC. The VGA/AGC combi-
nation 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 sin-
gle tri-level logic input. With no compression from the
AGC, 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 pre-
vents clipping at the output when too much gain is
applied 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 detect-
ing that the output voltage has exceeded a preset limit.
The microphone amplifier gain is then reduced with a
selectable time constant to correct for the excessive
output-voltage amplitude. This process is known as the
attack time. When the output signal subsequently low-
ers in amplitude, the gain is held at the reduced state
for a short period before slowly increasing to the nor-
mal value. This process is known as the hold and
release time. The speed at which the amplifiers adjust
to changing input signals is set by the external timing
capacitor CCT and the voltage applied to A/R. The
AGC threshold can be set by adjusting VTH. Gain
reduction is a function of input signal amplitude with a
maximum AGC attenuation of 20dB. Figure 2 shows the
effect of an input burst exceeding the preset limit, out-
put attack, hold and release times.
If the attack and release times are configured to
respond 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 to
accommodate the source material. For applications in
which music CDs are the main audio source, a 160µs
attack time with an 80ms release time is recommend-
ed. Music applications typically require a shorter
release time than voice or movie content.
Figure 1. Microphone Input with and Without AGC
MAX9814
Maxim Integrated
7
Attack Time
The attack time is the time it takes for the AGC to
reduce the gain after the input signal has exceeded the
threshold 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 when
a noticeable increase in loudness occurs. Short-
duration peaks are not reduced, but louder pas-
sages 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 the
threshold 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 the
set threshold level, and the attack time is reinitiated.
Release Time
The release time is how long it takes for the gain to
return to its normal level after the output signal has fall-
en 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 set-
ting after the input signal has fallen below the TH
threshold and the 30ms hold time has expired. Release
time is adjustable and has a minimum of 25ms. The
release time is set by picking an attack time using CCT
and setting the attack-to-release time ratio by configur-
ing A/R as shown in Table 1:
• Use a small ratio to maximize the speed of the AGC.
• Use a large ratio to maximize the sound quality and
prevent repeated excursions above the threshold
from being independently adjusted by the AGC.
AGC Output Threshold
The output threshold that activates AGC is adjustable
through the use of an external resistive divider. Once
the divider is set, AGC reduces the gain to match the
output voltage to the voltage set at the TH input.
Microphone Bias
The MAX9814 features an internal low-noise micro-
phone bias voltage capable of driving most electret
condenser microphones. The microphone bias is regu-
lated at 2V to provide that the input signal to the low-
noise preamplifier does not clip to ground.
Applications Information
Programming Attack and Release Times
Attack and release times are set by selecting the
capacitance value between CT and GND, and by set-
ting the logic state of A/R (Table 1). A/R is a tri-level
logic input that sets the attack-to-release time ratio.
The attack and release times can be selected by utiliz-
ing the corresponding capacitances listed in Table 2.
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
10ms/div
VCT
500mV/div
VMICOUT
(AC-COUPLED)
1V/div
ATTACK RELEASE
HOLD
0V
0V
A/R ATTACK/RELEASE RATIO
GND 1:500
VDD 1:2000
Unconnected 1:4000
Figure 2. Input Burst Exceeding AGC Limit
Table 1. Attack-and-Release Ratios
tRELEASE (ms)
CCT
tATTACK
(ms) A/R =
GND
A/R =
VDD
A/R =
UNCONNECTED
22nF
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
Table 2. Attack-and-Release Time
MAX9814
8
Maxim Integrated
Setting the AGC Threshold
To set the output-voltage threshold at which the micro-
phone output is clamped, an external resistor-divider
must be connected from MICBIAS to ground with the out-
put 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 and
remains 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 the
electret microphone. A value of 2.2kΩis usually sufficient
for a microphone of typical sensitivity. Consult the micro-
phone data sheet for the recommended bias resistor.
Bias Capacitor
The BIAS output of the MAX9814 is internally buffered
and 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 a
highpass 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 out-
puts. The -3dB point of the highpass filter, assuming
zero source impedance due to the input signal source,
is given by:
Choose CIN such that f-3dB_IN is well below the lowest
frequency of interest. Setting f-3dB_IN too high affects the
amplifier’s low-frequency response. Use capacitors with
low-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), can
result in increased distortion at low frequencies.
Output Capacitor
The output of the MAX9814 is biased at 1.23V. To elimi-
nate the DC offset, an AC-coupling capacitor (COUT)
must be used. Depending on the input resistance (RL)
of the following stage, COUT and RLeffectively form a
highpass filter. The -3dB point of the highpass filter,
assuming zero output impedance, is given by:
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, and
the 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 the
device as possible. Surface-mount components are
recommended. In systems where analog and digital
grounds are available, connect the MAX9814 to analog
ground.
f1
2RC
3dB_OUT L OUT
−=××π
f1
2R C
3dB_IN IN IN
−=××π
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
MAX9814
Maxim Integrated
9
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
Typical Application Circuit/Functional Diagram
AGC
MICBIAS
BIAS
RMICBIAS
2.21kΩ
R1
150kΩ
R2
100kΩ
MICIN COUT
GND
VDD
CIN
0.1μF
A/R
MICBIAS
GAIN
TH
MICOUT
VDD
VDD
SHDN
CBYPASS
1μF
CBIAS
0.47μF
CG
CCG
2.2μF
CT
CCT
470nF
REF
LNA VGA
ROUT
*THE DEVICE HAS BEEN CONFIGURED WITH AN ATTACK TIME OF 1.1ms, 40dB GAIN, AND AN ATTACK-AND-RELEASE RATIO OF 1:500.
MAX9814
MAX9814
10
Maxim Integrated
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
Chip Information
PROCESS: BiCMOS
Pin Configuration
MAX9814
TDFN
TOP VIEW
245
13 11 10
MICBIAS
N.C.
GAIN
SHDN
N.C.
VDD
1
14
+
THCT
3
12
BIASCG
6
9
A/RMICOUT
7
8
MICINGND
*EP
MAX9814
Maxim Integrated
11
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
COMMON DIMENSIONS
SYMBOL MIN. MAX.
A 0.70 0.80
D 2.90 3.10
E 2.90 3.10
A1 0.00 0.05
L0.200.40
PKG. CODE ND2 E2 eJEDEC SPEC b[(N/2)-1] x e
PACKAGE VARIATIONS
0.25 MIN.k
A2 0.20 REF.
2.00 REF0.25±0.05
0.50 BSC
2.30±0.1010
T1033-1
2.40 REF0.20±0.05- - - -
0.40 BSC
1.70±0.10 2.30±0.1014
T1433-1
1.50±0.10 MO229 / WEED-3
0.40 BSC - - - - 0.20±0.05 2.40 REFT1433-2 14 2.30±0.101.70±0.10
T633-2 61.50±0.10 2.30±0.10 0.95 BSC MO229 / WEEA 0.40±0.05 1.90 REF
T833-2 8 1.50±0.10 2.30±0.10 0.65 BSC MO229 / WEEC 0.30±0.05 1.95 REF
T833-3 8 1.50±0.10 2.30±0.10 0.65 BSC MO229 / WEEC 0.30±0.05 1.95 REF
2.30±0.10 MO229 / WEED-3 2.00 REF0.25±0.050.50 BSC1.50±0.1010
T1033-2
0.25±0.05 2.00 REF10 0.50 BSC MO229 / WEED-3
2.30±0.101.50±0.10
T1033MK-1
0.40 BSC - - - - 0.20±0.05 2.40 REFT1433-3F 14 2.30±0.101.70±0.10
Package Information (continued)
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages.
MAX9814
Maxim Integrated
13
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
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 1, 2, 6, 11
2 6/09 Removed UCSP package 1, 2, 6, 11, 12
MAX9814
14 Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000
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.
© Maxim Integrated The Maxim logo and Maxim Integrated are trademarks of Maxim Integrated Products, Inc.
