WM7220 Wolfson Microelectronics plc, WM7220 Datasheet - Page 5

• Manufacturer Part Number: WM7220
• Description: Digital Silicon Microphone
• Manufacturer: Wolfson Microelectronics plc

Preliminary Technical Data
ACOUSTIC AND ELECTRICAL CHARACTERISTICS
TERMINOLOGY
1.
2.
3.
4.
5.
6.
w
Test Conditions: VDD=1.8V, 1kHz test signal, CLK=2.4MHz, T
PARAMETER
Directivity
Sensitivity
Acoustic Overload
Signal to Noise Ratio
Total Harmonic Distortion
Frequency Response
Acoustic Noise Floor
Electrical Noise Floor
Power Supply Rejection
Digital Input / Output
CLK Input HIGH Level
CLK Input LOW Level
DAT Output HIGH Level
DAT Output LOW Level
Input capacitance (CLK)
Maximum load capacitance
(DAT)
Input Leakage
Short Circuit Output Current
Miscellaneous
Current Consumption
Start-up Time
CLK Sleep Frequency
Sensitivity (dBFS) - Sensitivity is a measure of the microphone output in response to the acoustic pressure of a 1kHz
94dB SPL (1Pa) sine wave. This is referenced to the Full Scale Range (FSR) of the microphone.
Signal-to-Noise Ratio (dB) – SNR is a measure of the difference in level between the output resulting from a 1kHz
SPL sine wave and the idle noise output.
Total Harmonic Distortion (dB) – THD is the level of the rms value of the sum of harmonic distortion products in the
specified bandwidth (see note below) relative to the amplitude of the fundamental (ie. test frequency) output.
All performance measurements carried out with 20kHz brick wall filter and, where noted, an A-weighted filter. Failure
to use such a filter will result in higher THD and lower SNR readings than are found in the Acoustic and Electrical
Characteristics. The brick wall filter removes out of band noise; although it is not audible, it affects dynamic
specification values.
Sensitivity and Electrical Noise Floor are measured in dBFS, relative to Full Scale Range (FSR). Full scale range is
the digital maximum full scale range reached when the part is excited by a 1kHz input test signal of 116dBSPL as the
test signal reaches full-scale amplitude. In general this is the large possible undistorted signal that will fit in the
numerical range. Because the definition of full scale range is based on a sine wave, it will be possible with square-
wave test signals to achieve +3,01dBFS.
SLEEP Mode is enabled when the CLK input is below the CLK Sleep Frequency noted above. This is a power saving
mode. Normal operation resumes automatically when the CLK input is above the CLK Sleep Frequency. Note that the
VDD supply is still required in SLEEP mode.
SYMBOL
C
SNR
THD
ENL
PSR
V
I
V
V
C
V
LOAD
I
VDD
S
SC
OH
OL
IH
IN
IL
DAT connected to GND
TEST CONDITIONS
+3dB High frequency
217Hz Square Wave
-3dB Low frequency
100mV pk-pk
SLEEP Mode
From SLEEP
Active Mode
A-Weighted
THD < 10%
I
100dB SPL
A-weighted
A-weighted
I
OH
From OFF
94dB SPL
OL
= +1mA
= -1mA
A
= 25°C
0.65 x
VDD
0.9 x
VDD
MIN
-29
Omni-directional
TYP
7800
120
650
-26
-86
0.1
5.0
58
35
36
70
50
10
PTD, Rev 2.0, October 2010
0.35 x
MAX
VDD
0.1 x
VDD
100
-23
1.0
10
10
1
1
WM7220
dB SPL
dB SPL
UNIT
dBFS
dBFS
dBFS
kHz
mA
ms
dB
μA
μA
Hz
Hz
pF
pF
%
V
V
V
V
5