SN8P2977
8-Bit Micro-Controller with Regulator, PGIA, 24-bit ADC
SONiX TECHNOLOGY CO., LTD
Page 111
Version 1.7
13.6 24-Bit Analog to Digital Converter (ADC)
The SN8P2977 integrated a 24-
bit ΔΣ Analog-to-Digital Converters (ADC) with decimation filters can be set for variable
throughputs range from 7.6 Hz up to 5.2 kHz. A reference voltage (Vref) is built in internal with selective range from
0.36V to 1.2V in AVDDR=2.4V condition, or an external reference voltage can be used to adjust an adequate range via
differential voltage between input pins of R+ and R-. The on-chip input buffers can be used to provide high input
impedance for direct connection to sensitive transducers. The ADC builds in internal Gain Option with selective range
of x1 and x2 for additional signal amplification expect PGIA.
ADC Modulator
Decimation
Filter
OSR[2:0]
Over Sampling Rate
OFSEL[1:0]
ADGN [1:0]
ADC Offset
ADC Gain
ADC Clk
Vref
X+
ADC Sturcture
0.36V 0100
0.60V 0101
0.84V 0110
1.20V 0111
* ...
* ...
External V(R+, R-)
R+
R-
0
1
RVS
0: External Vref (R+, R-)
1: Internla Vref
ADC
Output
Input Buffer
X-
ADCKS[2:0]
Over Sample Rate
OSR[2:0]
000: 64
001: 128
010: 256
011: 1024
100: 4096
101: 8192
110: 16384
111: 32768
ADC Offset
OFSEL[1:0]
00: -75% Vref
01: -50% Vref
10: -25% Vref
11: 0% Vref
Internal Vref
RVS [3:0]
0100: 0.36V
0101: 0.60V
0110: 0.84V
0111: 1.20V
RVS[3:0]
When AVDDR=2.4V
When AVDDR=2.4V
13.6.1
Analog Inputs and Voltage Operation Range
There are six analog inputs for ADC and PGIA operation, including pins of AI1, AI2, AI3, AI4,R+ and R-. The analog
inputs of PGIA, AI1/AI2-, AI3/AI4, are connected to external sensor
’s output signal, which can be configured as
differential mode (AI1 to AI2) or single-end (AI1 to AVE). External Vref for ADC is decided by differential voltage of
input pin R+ and R-. All of analog inputs are restricted in absolute voltage range between 0.4V to AVDDR-1V
(@AVDDR=2.4V). Moreover, the output signals of PGIA, X+/X-, must also remain within the absolute voltage range.
13.6.2
Reference Voltage
There are two reference voltage (Vref) sources option for ADC operation. One is from internal Vref another is from
external Vref. The ADC‟s Vref is selected using IRVS[3:0] bits in register ADCM1. Internal Vref source which can be
selected value from 0.225V~1.6V setting IRVS[3:0] bits. When IRVS3 & IRVS2 bit is setting
to „1‟, the Vref is from
external and the value is decided by differential voltage between Pins of R+ and R-. Detail setting reference register
ADCM1