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 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
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 TDFN (3mm x 3mm)
Packages
o -40°C to +85°C Extended Temperature Range
MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
________________________________________________________________
Maxim Integrated Products
1
Ordering Information
Simplified Block Diagram
LOW-NOISE
REFERENCE
AGC
2.7V TO 5.5V
LNA
+12dB
VGA
+20dB/0dB
GAIN
+8/+18/
+28dB
MICBIAS
R
MICBIAS
MICIN
OUT
C
OUT
GND
C
IN
V
DD
SHDN
MAX9814
PART
TEMP RANGE
PINPACKAGE
PKG
CODE
MAX9814EBC+T
B12-3
MAX9814ETD+T
T1433-2
19-0764; Rev 0; 3/07
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.
+
Denotes a lead-free package.
Pin Configurations appear at end of data sheet.
UCSP is a trademark of Maxim Integrated Products, Inc.
EVALUATION KIT
AVAILABLE
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
-40°C to +85°C 12 UCSP-12
-40°C to +85°C 14 TDFN-14
MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(V
DD
= 3.3V, SHDN = VDD, CCT= 470nF, CCG= 2µF, GAIN = VDD, TA= T
MIN
to T
MAX
, unless otherwise specified. Typical values are
at T
A
= +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.
VDDto GND..............................................................-0.3V to +6V
All Other Pins to GND.................................-0.3V to (V
DD
+ 0.3V)
Output Short-Circuit Duration.....................................Continuous
Continuous Current (OUT, MICBIAS) .............................±100mA
All Other Pins ....................................................................±20mA
Continuous Power Dissipation (T
A
= +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
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
GENERAL
Operating Voltage V
Supply Current I
Shutdown Supply Current I
Input-Referred Noise Density e
Output Noise BW = 20kHz 430 µV
Signal-to-Noise Ratio SNR
Dynamic Range DR (Note 2) 60 dB
Total Harmonic Distortion Plus
Noise
Amplifier Input BIAS V
Maximum Input Voltage V
Input Impedance Z
Maximum Gain A
Maximum Output Level V
Regulated Output Level AGC enabled, VTH = 0.7V 1.26 1.40 1.54 V
AGC Attack Time t
Attack/Release Ratio A/R
DD
DD
SHDN
n
THD+N
IN
IN_MAX
IN
OUT_RMS
ATTACK
Guaranteed by PSRR test 2.7 5.5 V
BW = 20kHz, all gain settings 30 nV/√Hz
BW = 22Hz to 22kHz
RMS
= 0.5mV
IN
), VIN = 30mV
P-P
DD
DD
DD
output signal)
RMS
(500mV
A-weighted 64
fIN = 1kHz, BW = 20Hz to 20kHz,
= 10kΩ, VTH = 1V (threshold = 2V
R
L
), V
P
= 1kHz, BW = 20Hz to 20kHz,
f
IN
= 10kΩ, VTH = 0.1V (threshold =
R
L
200mV
1% THD 100 mV
GAIN = V
GAIN = GND 49.5 50 50.6
GAIN = unconnected 59.5 60 60.5
GAIN = V
GAIN = GND 29.0 30 30.8Minimum Gain
GAIN = unconnected 38.7 40 40.5
1% THD+N, VTH = MICBIAS 0.707 V
CT = 470nF (Note 3) 1.1 ms
A/R = GND 1:500
A/R = V
A/R = unconnected 1:4000
, VCT = 0V
, VCT = 2V
RMS
P-
3.1 6 mA
0.01 1 µA
61
0.04
0.2
1.14 1.23 1.32 V
100 kΩ
39.5 40 40.5
18.7 20 20.5
1:2000
RMS
dB
%
P-P
dB
dB
RMS
P-P
ms/ms
MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
_______________________________________________________________________________________ 3
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 (0.707µV
RMS
), 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 V
MICOUT
= 1.23V.
Note 5: CG connected to GND with 2.2µF.
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= 3.3V, SHDN = VDD, CCT= 470nF, CCG= 2µF, GAIN = VDD, TA= T
MIN
to T
MAX
, unless otherwise specified. Typical values are
at T
A
= +25°C.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
MICOUT High Output Voltage V
MICOUT Low Output Voltage V
OH
OL
I
sourcing 1mA 2.45 V
OUT
I
sinking 1mA 3 mV
OUT
MICOUT Bias MICOUT unconnected 1.14 1.23 1.32 V
Output Impedance Z
Minimum Resistive Load R
Maximum Capacitive Drive C
Maximum Output Current I
Output Short-Circuit Current I
OUT
LOAD_MIN
LOAD_MAX
OUT_MAX
SC
1% THD, RL = 500Ω 12mA
AGC mode; VDD = 2.7V to 5.5V (Note 4) 35 50
Power-Supply Rejection Ratio PSRR
f = 217Hz, V
f = 1kHz, V
f = 10kHz, V
RIPPLE
RIPPLE
RIPPLE
MICROPHONE BIAS
Microphone Bias Voltage V
Output Resistance R
Output Noise Voltage V
MICBIAS_NOISEIMICBIAS
MICBIAS
MICBIAS
I
MICBIAS
I
MICBIAS
= 0.5mA 1.84 2.0 2.18 V
= 1mA 1 Ω
= 0.5mA, BW = 22Hz to 22kHz 5.5 µV
DC, VDD = 2.7V to 5.5V 70 80
Power-Supply Rejection Ratio PSRR
I
MICBIAS
f
IN
= 0.5mA, V
= 1kHz
TRILEVEL INPUTS (A/R, GAIN)
A/R or GAIN = V
Tri-Level Input Leakage Current
A/R or GAIN = GND
Input High Voltage V
Input Low Voltage V
Shutdown Enable Time t
Shutdown Disable Time t
IH
IL
ON
OFF
DIGITAL INPUT (SHDN)
SHDN Input Leakage Current -1 +1 µA
Input High Voltage V
Input Low Voltage V
IH
IL
AGC THRESHOLD INPUT (TH)
TH Input Leakage Current -1 +1 µA
= 100mV
= 100mV
= 100mV
RIPPLE
DD
50 Ω
5kΩ
200 pF
38 mA
(Note 5) 55
P-P
(Note 5) 52.5
P-P
(Note 5) 43
P-P
= 100mV
P-P
,
0.5V
DD
/ 180kΩ
0.5V
DD
/ 180kΩ
71
0.5V
DD
/ 100kΩ
0.5V
DD
/ 100kΩ
VDD x 0.7 V
VDD x 0.3 V
60 ms
40 ms
1.3 V
0.5V
DD
/ 50kΩ
0.5V
DD
/ 50kΩ
0.5 V
dB
RMS
dB
mA
MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
4 _______________________________________________________________________________________
Typical Operating Characteristics
(VDD= 5V, CCT= 470nF, CCG= 2.2µF, VTH= V
MICBIAS
x 0.4, GAIN = VDD(40dB), AGC disabled, no load, RL= 10kΩ, C
OUT
= 1µF,
T
A
= +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
V
RIPPLE
= 200mV
P-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
V
RIPPLE
= 200mV
P-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
I
MICBIAS
(mA)
V
MICBIAS
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
V
OUT
= 800mV
RMS
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT VOLTAGE
MAX9814 toc08
OUTPUT VOLTAGE (V
RMS
)
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 (µV
RMS
/√Hz)
1010.1
100
10
0.01 100
1000
1
MICIN AC-COUPLED
TO GND
MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
_______________________________________________________________________________________
5
Typical Operating Characteristics (continued)
(VDD= 5V, CCT= 470nF, CCG= 2.2µF, VTH= V
MICBIAS
x 0.4, GAIN = VDD(40dB), AGC disabled, no load, RL= 10kΩ, C
OUT
= 1µF,
T
A
= +25°C, unless otherwise noted.)
MICBIAS NOISE vs. FREQUENCY
10,000
/√Hz)
1000
RMS
100
MICBIAS NOISE (nV
10
10 100k
FREQUENCY (Hz)
V
vs. V
1.00
VTH = 1V
0.75
)
RMS
(V
0.50
OUT
V
0.25
VTH = 0.5V
0
0150
OUT
VTH = 0.75V
VIN (mV
RMS
10k1k100
IN
AGC ENABLED
GAIN = 1
10050
)
MAX9814 toc10
500mV/div
MAX9814 toc13
V
MICIN
10mV/div
0V
V
MICOUT
0V
1.00
0.75
)
RMS
(V
0.50
OUT
V
0.25
0
040
SMALL-SIGNAL PULSE RESPONSE
CL = 10pF
200µs/div
V
vs. V
OUT
IN
VTH = 1V
VTH = 0.75V
VTH = 0.5V
VIN (mV
RMS
AGC ENABLED
GAIN = 0
302010
)
MAX9814 toc11
MAX9814 toc14
V
SHDN
5V/div
0V
V
MICBIAS
2V/div
0V
V
MICOUT
1V/div
0V
1.00
0.75
)
RMS
(V
0.50
OUT
V
0.25
0
015
TURN-ON RESPONSE
V
VTH = 1V
VTH = 0.5V
20ms/div
vs. V
OUT
VTH = 0.75V
AGC ENABLED
GAIN = UNCONNECTED
VIN (mV
RMS
MAX9814 toc12
IN
MAX9814 toc15
105
)
V
MICOUT
500mV/div
ATTACK TIME
MAX9814 toc16
V
MICOUT
500mV/div
0V
C
= 47nF
CT
200µs/div
0V
ATTACK TIME
200µs/div
C
CT
= 100nF
MAX9814 toc17
V
500mV/div
MICOUT
0V
HOLD AND RELEASE TIME
C
CT
A/R = GND
20ms/div
MAX9814 toc18
= 47nF
MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
6 _______________________________________________________________________________________
Pin Description
Typical Operating Characteristics (continued)
(VDD= 5V, CCT= 470nF, CCG= 2.2µF, VTH= V
MICBIAS
x 0.4, GAIN = VDD(40dB), AGC disabled, no load, RL= 10kΩ, C
OUT
= 1µF,
T
A
= +25°C, unless otherwise noted.)
HOLD AND RELEASE TIME
V
MICOUT
500mV/div
0V
C
= 47nF
CT
A/R = V
DD
40ms/div
PIN
TDFN UCSP
1A1 CT
2B2SHDN Active-Low Shutdown Control
3 A2 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.
5A3 VDDPower Supply. Bypass to GND with a 1µF capacitor.
6 A4 MICOUT Amplifier Output
7 B4 GND Ground
8 C4 MICIN Microphone Noninverting Input
9 B3 A/R
10 C3 GAIN
12 C2 BIAS Amplifier Bias. Bypass to GND with a 0.47µF capacitor.
13 C1 MICBIAS Microphone Bias Output
14 B1 TH
NAME FUNCTION
Timing Capacitor Connection. Connect a capacitor to CT to control the Attack and Release times of
the AGC.
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 = V
A/R = BIAS: Attack/Release Ratio is 1:4000
Tri-Level Amplifier Gain Control.
GAIN = V
GAIN = GND, gain set to 50dB.
GAIN = Unconnected, uncompressed gain set to 60dB.
AGC Threshold Control. TH voltage sets gain control threshold. Connect TH to MICBIAS to disable
the AGC.
: Attack/Release Ratio is 1:2000
DD
, gain set to 40dB.
DD
MAX9814 toc19
V
MICOUT
500mV/div
HOLD AND RELEASE TIME
MAX9814 toc20
0V
C
= 47nF
CT
A/R = UNCONNECTED
100ms/div
MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
_______________________________________________________________________________________ 7
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 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 CCTand 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.
Figure 1. Microphone Input with and Without AGC
MAX9814 AGC DISABLED
0V
0V
400µs/div
MAX9814 fig01a
V
100mV/div
V
(AC-COUPLED)
1V/div
MICIN
MICOUT
MAX9814 AGC ENABLED
0V
0V
400µs/div
MAX9814 fig01b
V
MICIN
100mV/div
V
MICOUT
(AC-COUPLED)
1V/div
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 C
CT
seconds (where CCTis 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 C
CT
and setting the attack-to-release time ratio by configuring 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 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.
The attack and release times can be selected by utilizing the corresponding capacitances listed in Table 2.
MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
8 _______________________________________________________________________________________
Figure 2. Input Burst Exceeding AGC Limit
Table 1. Attack-and-Release Ratios
t
RELEASE
(ms)
C
CT
t
ATTACK
(ms)
A/R =
GND
A/R =
V
DD
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
ATTACK
0V
0V
HOLD
RELEASE
V
CT
500mV/div
V
MICOUT
(AC-COUPLED)
1V/div
10ms/div
A/R ATTACK/RELEASE RATIO
GND 1:500
V
DD
Unconnected 1:4000
1:2000
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 V
TH
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 V
TH
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
R
MICBIAS
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
). CINprevents 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:
Choose C
IN
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 (C
OUT
)
must be used. Depending on the input resistance (R
L
)
of the following stage, C
OUT
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.
MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
_______________________________________________________________________________________ 9
f
3dB_IN
−
=
1
××π
2R C
IN IN
f
3dB_OUT
−
=
2RC
1
××π
L OUT
MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
10 ______________________________________________________________________________________
Typical Application Circuit/Functional Diagram
V
DD
C
BYPASS
1µF
C
BIAS
0.47µF
R
MICBIAS
2.21kΩ
C
CT
47nF
C
CG
2.2µF
*THE DEVICE HAS BEEN CONFIGURED WITH AN ATTACK TIME OF 1.1ms, 40dB GAIN, AND AN ATTACK-AND-RELEASE RATIO OF 1:500.
C
0.1µF
SHDN
V
DD
MICBIAS
MAX9814
BIAS
MICBIAS
MICIN
IN
CT
CG
LNA
REF
AGC
VGA
GND
A/R
GAIN
OUT
R
1
150kΩ
TH
V
DD
C
OUT
R
2
100kΩ
R
OUT
MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
______________________________________________________________________________________ 11
Chip Information
PROCESS: BiCMOS
Pin Configurations
UCSP
TOP VIEW
(BUMP SIDE DOWN)
MAX9814
1234
CT CG V
DD
MICOUT
TH SHDN A/R GND
MICBIAS BIAS GAIN MICIN
B
A
C
MAX9814
TDFN
TOP VIEW
245
13 11 10
MICBIAS
N.C.
GAIN
SHDN
N.C.
V
DD
1
14
+
THCT
3
12
BIASCG
6
9
A/RMICOUT
7
8
MICINGND
MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
12 ______________________________________________________________________________________
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
.)
PACKAGE OUTLINE, 4x3 UCSP
21-0104
12L, UCSP 4x3.EPS
1
F
1
MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
______________________________________________________________________________________ 13
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
.)
6, 8, &10L, DFN THIN.EPS
MAX9814
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
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.
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
SYMBOL MIN. MAX.
A 0.70 0.80
D 2.90 3.10
E 2.90 3.10
0.00 0.05
A1
L 0.20 0.40
A2 0.20 REF.
PACKAGE VARIATIONS
PKG. CODE N D2 E2 e JEDEC SPEC b
T633-2 6 1.50±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
1.50±0.10 MO229 / WEED-3
2.30±0.10 MO229 / WEED-3 2.00 REF0.25±0.050.50 BSC1.50±0.1010T1033-2
0.25 MIN.k
0.40 BSC - - - - 0.20±0.05 2.40 REFT1433-2 14 2.30±0.101.70±0.10
[(N/2)-1] x e
2.00 REF0.25±0.050.50 BSC2.30±0.1010T1033-1
2.40 REF0.20±0.05- - - - 0.40 BSC1.70±0.10 2.30±0.1014T1433-1
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