WM8737L

Preliminary Technical Data

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AI Rev 3.0 May 2004

8

Test Conditions

audio data, unless otherwise stated.

PARAMETER

SYMBOL

TEST CONDITIONS

MIN

TYP

MAX

UNIT

Analogue Reference Levels

Mid-rail Reference Voltage

VMID

–3%

AVDD/2

+3%

V

VMID Output Resistance

75

k

Ω

Buffered Reference Voltage

VREF

–3%

AVDD/2

+3%

V

Microphone Bias

MICBIAS = 01

0.75

×AVDD

V

MICBIAS = 10

0.9

×AVDD

–3%

0.9

×AVDD

0.9

×AVDD

+3%

V

Bias Voltage

MICBIAS = 11,

AVDD = 2.5V

1.2

×AVDD

V

Bias Current Source

3

mA

Output Noise Voltage

Vn

1K to 20kHz

24

nV/

√Hz

Digital Input / Output

Input HIGH Level

0.7

×DBVDD

V

Input LOW Level

0.3

×DBVDD

V

Output HIGH Level

0.9

×DBVDD

V

Output LOW Level

0.1

×DBVDD

V

TERMINOLOGY

1.

Signal-to-noise ratio (dB) – for the microphone preamplifiers, quoted SNR is the ratio of the rms voltages of the full-

scale output at the L/RACOUT pins and the noise observed at these pins with no input signals. This figure indicates

only the microphone preamplifier noise and does not account for additional noise that will be added by the PGAs and

ADCs in obtaining the final digitised result. For the line inputs, quoted SNR is the ratio of the rms code ranges as

measured at the ADC output for a full-scale output signal and the noise observed with no input. This figure combines

the PGA and ADC noise contributions. (No Auto-zero or Auto-mute function is employed in achieving these results).

2.

Dynamic range (dB) - DR measures the ratio in the ADC output between the full-scale signal power and all power

contributed by noise and spurious tones in the specified bandwidth. Normally THD+N is measured at 60dB below full

scale (to reduce any distortion components to negligible levels) and the measurement is then corrected by adding the

60dB to its magnitude. (e.g. THD+N @ -60dB= -32dB, DR= 60 + |-32| = 92dB).

3.

Total Harmonic Distortion and Noise (dB) - THD+N is a ratio of the rms values of (Noise + Distortion) and Signal.

4.

Channel Separation (dB) - Also known as Cross-Talk. This is a measure of the amount one channel is isolated from

the other. Normally measured by sending a full scale signal down one channel and measuring how much of this

signal appears at the output of the other channel.

5.

Hold Time is the length of time between a signal detected by the ALC as being too quiet and beginning to ramp up

the gain. It does not apply to ramping down the gain when the signal is too loud, which happens without a delay.

6.

Ramp-up and Ramp-Down times are defined as the time it takes for the PGA to sweep across 90% of its gain range.

7.

All hold, ramp-up and ramp-down times scale proportionally with MCLK

NOTES

1.

All performance measurements are done with a 20kHz low pass filter, and where noted an A-weight filter. Failure to

use such a filter will result in higher THD+N and lower SNR and Dynamic Range readings than are found in the

Electrical Characteristics. The low pass filter removes out of band noise; although this is not audible, it may affect

dynamic specification values.

2.

VMID and VREF are each to be decoupled to a clean analogue ground with 10uF and 0.1uF capacitors placed as

close to the device package as possible. Smaller capacitors may reduce performance. VREFP should be connected

to VREF and VREFN should be connected to AGND using short PCB traces. It is not recommended to connect other

components to VMID or VREF in case of noise injection to the internal references of the device.