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MAX4063ETE+

P1-P3P4-P6P7-P9P10-P12P13-P14
MAX4063
Differential Microphone Preamplifier with
Internal Bias and Complete Shutdown
_______________________________________________________________________________________ 7
Detailed Description
The MAX4063 is a differential microphone pre-
amplifier providing high-quality amplification, optimized
for use in computer and mobile applications. This device
features adjustable gain, very high power-supply rejec-
tion (95dB), and common-mode rejection (79dB), making
it ideal for low-noise applications. The MAX4063 provides
a differential input stage, making the device particularly
effective when layout constraints force the microphone
amplifier to be physically remote from the ECM micro-
phone.
The MAX4063 is capable of switching its output
between the differential input and an inverting single-
ended input. INT/AUX selects either the differential
input or single-ended auxiliary input. In addition, the
MAX4063 has an integrated microphone bias source,
simplifying system design and eliminating the need for
external components. The MAX4063 has a complemen-
tary output allowing CODECs and other devices with
differential inputs to be optimally driven (see
Functional
Diagram
). The MAX4063 includes a 0.3µA shutdown
mode for ultimate power savings. The differential gain
of the MAX4063 is set with a single resistor connected
between the G1 and G2 pins. The MAX4063 has an
internal default gain of 20V/V on the AUX_IN input. The
AUX_IN gain can be increased with a single external
resistor (see the
Differential-Gain Adjustment and
Auxiliary Input-Gain Adjustment
sections).
Differential Input
The main microphone amplifier is a low-noise, differen-
tial input structure. This is an almost essential element
when faced with amplification of low-amplitude analog
signals in digitally intense environments such as note-
PIN
TSSOP TQFN
NAME FUNCTION
115 G2
Gain-Selectable Input. Connect an external resistor between G1 and G2 to set the gain for
the differential amplifier (see Adjustable Differential Gain-Setting section).
216INT/AUX
Internal (Differential) or Auxiliary (Single-Ended) Input Select. Drive INT/AUX low to select
differential in or high to select auxiliary in.
31SHDN
Shutdown Input. Drive SHDN high for normal operation. Drive SHDN low for shutdown
mode.
4 2 OUT Amplifier Output. OUT is high impedance when in shutdown mode.
5 3 BIAS
External Electret Microphone Capsule Bias Output. Bypass BIAS with a 1µF capacitor to
ground.
64V
CC
Power Supply. Bypass the V
CC
to GND with a 0.1µF capacitor.
7 5 ADJ
Adjustable Gain Select for AUX_IN (see Auxiliary Input-Gain Adjustment section). Connect
a 10pF capacitor between OUT and ADJ.
87OUT Complementary Amplifier Output. OUT is high impedance in shutdown mode.
9 9 IN+ Noninverting Differential Amplifier Input. AC-couple the audio signal into IN+.
10 10 IN- Inverting Differential Amplifier Input. AC-couple the audio signal into IN-.
11 11 GND Ground
12 12 AUX_IN Single-Ended Input for Auxiliary Microphone. AC-couple the audio signal into AUX_IN.
13 6, 8, 14 N.C. No Connection. Not internally connected.
14 13 G1
Gain-Selectable Input. Connect an external resistor between G1 and G2 to set the gain for
the differential amplifier.
—— EP
Exposed Pad (TQFN Only). Internally connected to GND. Connect to a large ground plane
to maximize thermal performance. Not intended as an electrical connection point.
Pin Description
MAX4063
Differential Microphone Preamplifier with
Internal Bias and Complete Shutdown
8 _______________________________________________________________________________________
book PCs or PDAs. Used correctly, the advantages
over a single-ended solution are:
• Better power-supply noise rejection.
• Less degradation from noise in PC board ground
planes.
• The microphone and preamplifier may be placed
physically further apart, easing PC board layout
restrictions.
Differential-Gain Adjustment
The MAX4063 allows the user to alter the differential
gain to optimize the signal-to-noise ratio (SNR) of their
system. The gain is set by a single external resistor
(R
G
) connected between the G1 and G2 pins:
where A
V
is the required voltage gain.
Hence, an 11.11kΩ resistor yields a gain of 20V/V, or
26dB. Leaving the pins unconnected results in a gain of
2V/V. Gain is defined as:
For differential out:
The resistor can be either fixed or variable, allowing the
use of a digitally controlled potentiometer to alter the
gain under software control.
Auxiliary Input-Gain Adjustment
The MAX4063 provides an option to increase the
AUX_IN (see Figure 3). To increase the gain, connect
resistor R
ADJ
between the ADJ and AUX_IN pins. R
ADJ
is
calculated from the following formula:
R
2M
AV
ADJ
AUX
=
−
Ω
20
()to increase the gain
A
V
V
VD
OUT OUT
IN+ IN-
=
−
−
V
V
R
200k
A
G
VD
=
−
Ω
2
BIAS
BIAS
AUX_IN
12
IN-
IN+
10
9
6
V
CC
2.4V TO 5.5V
MAX4063
2INT/AUX
8OUT
OUT
ADJ
4
7
GND
11
SHDN
SHDN
V
CC
3
BIAS
5
V
BIAS
G2
G1
1
14
R
G
Functional Diagram
MAX4063
Differential Microphone Preamplifier with
Internal Bias and Complete Shutdown
_______________________________________________________________________________________ 9
where:
R
ADJ
is placed between AUX_IN and ADJ.
Input Capacitors
The two differential microphone inputs and the single-
ended auxiliary input of the MAX4063 have on-chip
bias components, allowing the user to AC-couple any
signals into the input. The input resistance is 100kΩ
(typ), so the capacitor size may be chosen accordingly
to define the LF rolloff desired. This can be calculated
as:
C
IN
= 1 / (2πf
CUT
R
IN
)
This assumes a low source impedance is driving the
inputs.
A further consideration for the differential input is the
effect of these series input capacitors on low-frequency,
common-mode rejection. Any mismatch in the values of
these two capacitors degrades the CMRR at frequen-
cies where the impedance of the capacitor is significant
compared to the input resistance of the amplifier—this is
usually most noticeable at low frequencies. One way to
avoid the need for matched or tight tolerance capaci-
tors is to deliberately oversize the values on the differ-
ential inputs and to set the lower 3dB point (f
CUT
) of the
amplifier by sizing the output capacitor appropriately.
The input impedance matching on the differential input
is typically 1%, allowing input capacitor matching to be
effective at improving low-frequency PSRR.
Common-Mode Rejection Ratio
The common-mode rejection ratio (CMRR) refers to the
amount of rejection that the amplifier is capable of pro-
viding to any signal applied equally to the IN+ and IN-
inputs. In the case of amplifying low-level microphone
signals in noisy digital environments, it is a key figure of
merit. In audio circuits, this is generally measured for
V
IN
as an AC signal:
CMRR(dB) = A
DM
/ A
CM
where A
DM
is the differential gain, A
CM
is the common-
mode gain.
Input voltages should be sufficiently small such that the
output is not clipped in either differential or common-
AV
V
V
AUX
OUT OUT
AUX_IN
=
− V
Figure 1. MAX4063 with Auxiliary Input Configuration
ADJ
7
AUX_IN
12
5
IN-
IN+
10
9
6
V
CC
2.4V TO 5.5V
MAX4063
2
INT/AUX
8OUT
OUT
4
GND
11
SHDN
V
BIAS
SHDN
V
CC
3
G2
G1
BIAS
1
14
R
BIAS
C
BIAS
100kΩ
P1-P3P4-P6P7-P9P10-P12P13-P14

MAX4063ETE+

Mfr. #:
Buy MAX4063ETE+
Manufacturer:
Maxim Integrated
Description:
Microphone Preamplifiers Differential Mic Preamplifier
Lifecycle:
New from this manufacturer.
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