Preliminary
SPCA751A-P101
! 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 (TA = 25ºC, VDD = 3.3 V)
PARAMETER
ATO:
Input Voltage
PGA:
Gain Range
Step Size
Step Variation
Voltage Reference:
Output Voltage
CONDITION
MA gain = 0dB,
PGA gain = 6dB
Default: 6dB
MIN.
TYP.
MAX. UNIT
0.25*VDD Vpp
-12
6
0.5
12
dB
dB
dB
0.45VDD 0.5VDD 0.55VDD Vpp
ADC PATH CHARACTERISTICS
PARAMETER
ADC:
Signal to noise ratio
CONDITION
FIN = 1kHz,
PGA gain = 12dB
ATO is full swing
Without data compression
MIN.
TYP.
60
MAX. UNIT
dB
7