Preliminary

SPCA751A-P101

7

!

ADC

The SPCA751A has an audio-band sigma-delta analog-to-digital converter so as to meet the

requirement of the digital recorder application. The circuit of converter consists of two main blocks: the analog-

to-digital converter (ADC) and internal reference and bias voltage. For the latter, it is 15-bit format with 10-bit

resolution.

The analog-to-digital conversion chain consists of a microphone amplifier (M.A.), a programmable gain

amplifier (PGA), an analog oversampled modulator, and the decimation digital filter. The PGA has gain step

from –12dB to 12dB (-12, -6, 0, 6, 12dB). The modulator is a sigma-delta feedback loop, which oversamples the

signal at 1.024MHz and provides second-order noise shaping. It performs the conversion of the differential

analog input signal to a pulse-density-modulated single-bit digital output. When a maximum positive differential

input voltage is applied at the input of modulator, the resulting code at the output of the modulator is all ones.

The decimation digital filter consists of a comb filter and a half-band filter. The comb filter is a third-order comb

filter. Finally the encoder implements the half-band filter and data compression by software.

ADC & DAC ELECTRICAL CHARACTERISTICS (T

PARAMETER

CONDITION

MIN.

TYP.

MAX.

UNIT

ATO:

Input Voltage

MA gain = 0dB,

PGA gain = 6dB

0.25*VDD

Vpp

PGA:

Gain Range

Step Size

Step Variation

Default: 6dB

-12

6

0.5

12

dB

dB

dB

Voltage Reference:

Output Voltage

0.45VDD

0.5VDD

0.55VDD

Vpp

ADC PATH CHARACTERISTICS

PARAMETER

CONDITION

MIN.

TYP.

MAX.

UNIT

ADC:

Signal to noise ratio

F

PGA gain = 12dB

ATO is full swing

Without data compression

60

dB