MAXIM MAX9814

19-0764; Rev 0; 3/07
KIT
ATION
EVALU
E
L
B
AVAILA
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
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 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-biasvoltage generator can bias most electret microphones.
The MAX9814 is available in the space-saving 12-bump
UCSP™ (1.5mm x 2mm) and 14-pin TDFN packages.
This device is specified over the -40°C to +85°C
extended temperature range.
Applications
Digital Still Cameras
Digital Video Cameras
Two-Way Communicators
PDAs
Bluetooth Headsets
Entertainment Systems
(e.g., Karaoke)
Features
o Automatic Gain Control (AGC)
o Three Gain Settings (40dB, 50dB, 60dB)
o Programmable Attack Time
o Programmable Attack and Release Ratio
o 2.7V to 5.5V Supply Voltage Range
o Low Input-Referred Noise Density of 30nV/√Hz
o Low THD: 0.04% (typ)
o Low-Power Shutdown Mode
o Internal Low-Noise Microphone Bias, 2V
o Available in the Space-Saving 12-Bump UCSP
(1.5mm x 2mm) and 14-Pin TDFN (3mm x 3mm)
Packages
o -40°C to +85°C Extended Temperature Range
Ordering Information
PART
TEMP RANGE
PINPACKAGE
PKG
CODE
MAX9814EBC+T
-40°C to +85°C 12 UCSP-12
B12-3
MAX9814ETD+T
-40°C to +85°C 14 TDFN-14
T1433-2
High-Quality Portable
Recorders
+Denotes a lead-free package.
IP Phones/Telephone
Conferencing
Pin Configurations appear at end of data sheet.
UCSP is a trademark of Maxim Integrated Products, Inc.
Simplified Block Diagram
2.7V TO 5.5V
SHDN
MICBIAS
LOW-NOISE
REFERENCE
VDD
MAX9814
AGC
RMICBIAS
CIN
MICIN
LNA
+12dB
VGA
+20dB/0dB
GAIN
+8/+18/
+28dB
COUT
OUT
GND
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1
MAX9814
General Description
MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
ABSOLUTE MAXIMUM RATINGS
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 (OUT, MICBIAS) .............................±100mA
All Other Pins ....................................................................±20mA
Continuous Power Dissipation (TA = +70°C)
12-Bump UCSP (derate 6.5mW/°C above +70°C).......518mW
14-Pin TDFN (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)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
GENERAL
Operating Voltage
VDD
5.5
V
Supply Current
IDD
3.1
6
mA
ISHDN
0.01
1
µA
Shutdown Supply Current
Input-Referred Noise Density
2.7
BW = 20kHz, all gain settings
30
nV/√Hz
Output Noise
BW = 20kHz
430
µVRMS
Signal-to-Noise Ratio
BW = 22Hz to 22kHz
(500mVRMS output signal)
61
A-weighted
64
(Note 2)
60
Dynamic Range
Total Harmonic Distortion Plus
Noise
Amplifier Input BIAS
Maximum Input Voltage
Input Impedance
Maximum Gain
en
Guaranteed by PSRR test
SNR
DR
THD+N
Attack/Release Ratio
2
fIN = 1kHz, BW = 20Hz to 20kHz,
RL = 10kΩ, VTH = 0.1V (threshold =
200mVP-P), VIN = 30mVRMS, VCT = 2V
0.2
A
VOUT_RMS
1.14
1% THD
A/R
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
CT = 470nF (Note 3)
40.5
0.707
1.26
V
100
GAIN = VDD
AGC enabled, VTH = 0.7V
tATTACK
dB
%
ZIN
Regulated Output Level
AGC Attack Time
0.04
VIN
VIN_MAX
Minimum Gain
Maximum Output Level
fIN = 1kHz, BW = 20Hz to 20kHz,
RL = 10kΩ, VTH = 1V (threshold = 2VPP), VIN = 0.5mVRMS, VCT = 0V
dB
1.40
1.1
A/R = GND
1:500
A/R = VDD
1:2000
A/R = unconnected
1:4000
_______________________________________________________________________________________
dB
dB
VRMS
1.54
VP-P
ms
ms/ms
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
(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)
PARAMETER
SYMBOL
CONDITIONS
MICOUT High Output Voltage
VOH
IOUT sourcing 1mA
MICOUT Low Output Voltage
VOL
IOUT sinking 1mA
MICOUT Bias
MICOUT unconnected
MIN
1.14
TYP
MAX
UNITS
2.45
V
3
mV
1.23
1.32
V
ZOUT
50
Ω
Minimum Resistive Load
RLOAD_MIN
5
kΩ
Maximum Capacitive Drive
CLOAD_MAX
200
pF
Output Impedance
Maximum Output Current
Output Short-Circuit Current
IOUT_MAX
1% THD, RL = 500Ω
ISC
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)
2
55
f = 1kHz, VRIPPLE = 100mVP-P (Note 5)
52.5
f = 10kHz, VRIPPLE = 100mVP-P (Note 5)
43
mA
mA
dB
MICROPHONE BIAS
Microphone Bias Voltage
Output Resistance
Output Noise Voltage
VMICBIAS
IMICBIAS = 0.5mA
RMICBIAS
IMICBIAS = 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 / 50kΩ
A/R or GAIN = GND
0.5VDD 0.5VDD 0.5VDD
/ 180kΩ / 100kΩ / 50kΩ
mA
Tri-Level Input Leakage Current
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
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
-1
Devices are production tested at TA = +25°C. Limits over temperature are guaranteed by design.
Dynamic range is calculated using the EIAJ method. The input is applied at -60dBFS (0.707µVRMS), fIN = 1kHz.
Attack time measured as time from AGC trigger to gain reaching 90% of its final value.
CG is connected to an external DC voltage source, and adjusted until VMICOUT = 1.23V.
CG connected to GND with 2.2µF.
_______________________________________________________________________________________
3
MAX9814
ELECTRICAL CHARACTERISTICS (continued)
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 = 0
30
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. FREQUENCY
GAIN 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 CURRENT
SHUTDOWN 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. FREQUENCY
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT VOLTAGE
INPUT-REFERRED NOISE
vs. FREQUENCY
1
fIN = 300Hz, 1kHz,
and 3kHz
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-COUPLED
TO GND
MAX9814 toc09
2.5
THD+N (%)
MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
100
10
1
0
0.5
1.0
OUTPUT VOLTAGE (VRMS)
1.5
0.01
0.1
1
FREQUENCY (kHz)
_______________________________________________________________________________________
10
100
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
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
10,000
VSHDN
5V/div
0V
VMICOUT
500mV/div
VMICBIAS
2V/div
0V
0V
VMICOUT
1V/div
0V
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
VTH = 0.75V
VTH = 0.75V
0.25
0.25
0.25
VTH = 0.5V
VTH = 0.5V
VTH = 0.5V
AGC ENABLED
GAIN = 1
0
50
150
100
AGC ENABLED
GAIN = UNCONNECTED
AGC ENABLED
GAIN = 0
0
0
10
20
30
0
0
40
5
15
10
VIN (mVRMS)
VIN (mVRMS)
VIN (mVRMS)
ATTACK TIME
ATTACK TIME
HOLD AND RELEASE TIME
VMICOUT
500mV/div
VMICOUT
500mV/div
0V
0V
VMICOUT
500mV/div
0V
CCT = 47nF
A/R = GND
CCT = 100nF
CCT = 47nF
200µs/div
MAX9814 toc18
MAX9814 toc16
0
0.50
MAX9814 toc17
VOUT (VRMS)
VOUT vs. VIN
VOUT vs. VIN
1.00
MAX9814 toc15
VOUT vs. VIN
1.00
200µs/div
20ms/div
_______________________________________________________________________________________
5
MAX9814
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.)
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 toc20
HOLD AND RELEASE TIME
MAX9814 toc19
MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
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
TDFN
UCSP
1
A1
CT
2
B2
SHDN
Timing Capacitor Connection. Connect a capacitor to CT to control the Attack and Release times of
the AGC.
Active-Low Shutdown Control
3
A2
CG
4, 11
—
N.C.
No Connection. Connect to GND.
5
A3
VDD
Power Supply. Bypass to GND with a 1µF capacitor.
6
A4
MICOUT
7
B4
GND
8
C4
MICIN
9
6
FUNCTION
B3
A/R
Amplifier DC Offset Adjust. Connect a 2.2µF capacitor to GND to ensure zero offset at the output.
Amplifier Output
Ground
Microphone Noninverting Input
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 = BIAS: Attack/Release Ratio is 1:4000
10
C3
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
C2
BIAS
Amplifier Bias. Bypass to GND with a 0.47µF capacitor.
13
C1
MICBIAS
14
B1
TH
Microphone Bias Output
AGC Threshold Control. TH voltage sets gain control threshold. Connect TH to MICBIAS to disable
the AGC.
_______________________________________________________________________________________
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
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 is
buffered 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 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 prevents 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 detecting 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 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 and
release 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 a
maximum AGC attenuation of 20dB. Figure 2 shows the
effect of an input burst exceeding the preset limit, output 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 recommended. Music applications typically require a shorter
release 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/div
0V
400µs/div
VMICIN
100mV/div
VMICOUT
(AC-COUPLED)
1V/div
400µs/div
Figure 1. Microphone Input with and Without AGC
_______________________________________________________________________________________
7
MAX9814
Detailed Description
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
MAX9814
and 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 and
prevent repeated excursions above the threshold
from being independently adjusted by the AGC.
RELEASE
0V
VMICOUT
(AC-COUPLED)
1V/div
0V
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
10ms/div
Figure 2. Input Burst Exceeding AGC Limit
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. 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 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 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. Release
time is adjustable and has a minimum of 25s. The
release time is set by picking an attack time using CCT
8
The MAX9814 features an internal low-noise microphone bias voltage capable of driving most electret
condenser 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 the
capacitance 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
1:2000
Unconnected
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
_______________________________________________________________________________________
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
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 2.2kΩ 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 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 outputs. The -3dB point of the highpass filter, assuming
zero source impedance due to the input signal source,
is given by:
f−3dB_IN =
1
2π × RIN × CIN
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 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 a
highpass 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, 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.
_______________________________________________________________________________________
9
MAX9814
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 and
remains at that level until the amplitude of the input signal
is reduced. To disable AGC, connect TH to MICBIAS.
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
MAX9814
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
OUT
CIN
0.1µF
COUT
ROUT
CT
CCT
47nF
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
______________________________________________________________________________________
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
TOP VIEW
(BUMP SIDE DOWN)
TH
MICBIAS
BIAS
N.C.
GAIN
A/R
MICIN
TOP VIEW
14
13
12
11
10
9
8
MAX9814
1
2
3
4
CT
CG
VDD
MICOUT
TH
SHDN
A/R
GND
MICBIAS
BIAS
GAIN
MICIN
A
B
MAX9814
C
5
6
7
GND
CG
4
MICOUT
3
VDD
2
N.C.
1
CT
UCSP
SHDN
+
TDFN
Chip Information
PROCESS: BiCMOS
______________________________________________________________________________________
11
MAX9814
Pin Configurations
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
12L, UCSP 4x3.EPS
MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
PACKAGE OUTLINE, 4x3 UCSP
21-0104
12
______________________________________________________________________________________
F
1
1
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
6, 8, &10L, DFN THIN.EPS
______________________________________________________________________________________
13
MAX9814
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
COMMON DIMENSIONS
PACKAGE VARIATIONS
SYMBOL
MIN.
MAX.
PKG. CODE
N
D2
E2
e
JEDEC SPEC
b
[(N/2)-1] x e
A
0.70
0.80
T633-2
6
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
T833-2
8
1.50±0.10
2.30±0.10
0.65 BSC
MO229 / WEEC
0.30±0.05
1.95 REF
E
2.90
3.10
T833-3
8
1.50±0.10
2.30±0.10
0.65 BSC
MO229 / WEEC
0.30±0.05
1.95 REF
A1
0.00
0.05
T1033-1
10
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
T1033-2
10
1.50±0.10
2.30±0.10
0.50 BSC
MO229 / WEED-3
0.25±0.05
2.00 REF
k
0.25 MIN.
T1433-1
14
1.70±0.10
2.30±0.10
0.40 BSC
----
0.20±0.05
2.40 REF
A2
0.20 REF.
T1433-2
14
1.70±0.10
2.30±0.10
0.40 BSC
----
0.20±0.05
2.40 REF
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.
14 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2007 Maxim Integrated Products
is a registered trademark of Maxim Integrated Products, Inc.