XE8805 SEMTECH [Semtech Corporation], XE8805 Datasheet - Page 90

• Manufacturer Part Number: XE8805
• Description: Data Acquisition MCU
• Manufacturer: SEMTECH [Semtech Corporation]

16.4 ZoomingADC™ Description
Figure 16-2 gives a more detailed description of the acquisition chain.
16.4.1
Figure 16-1 shows the general block diagram of the acquisition chain (AC). A control block (not shown in Figure
16-1) manages all communications with the CoolRisc™ microcontroller.
differential channels.
The core of the zooming section is made of three differential programmable amplifiers (PGA). After selection of a
combination of input and reference signals V
stages 1 to 3. Fine gain programming up to 1'000V/V is possible. In addition, the last two stages provide
programmable offset. Each amplifier can be bypassed if needed.
The output of the PGA stages is directly fed to the analog-to-digital converter (ADC), which converts the signal
V
Like most ADCs intended for instrumentation or sensing applications, the ZoomingADC™ is an over-sampled
converter (See Note
positive and negative input voltages). In first approximation, the ADC output result relative to full-scale (FS) delivers
the quantity:
1 Note: Over-sampled converters are operated with a sampling frequency f
1'000 times the input signal bandwidth). The sampling frequency to throughput ratio is large (typically 10-500). These converters include digital
decimation filtering. They are mainly used for high resolution, and/or low-to-medium speed applications.
© Semtech 2006
Analog inputs can be selected among eight input channels, while reference input is selected between two
IN,ADC
into digital.
pos.
pos.
pos.
6:0
6:0
5:1
7
7
7
6
0
Acquisition Chain
RegAcCfg3
RegAcCfg4
RegAcCfg5
PGA3_OFFSET[6:0]
PGA3_GAIN[6:0]
PGA1_GAIN
AMUX[4:0]
1
reserved
). The ADC is a so-called incremental converter, with bipolar operation (the ADC accepts both
VMUX
BUSY
DEF
rw
r w
r w
rw
r
r w
rw
r
w r0
r w
r w
0 resetsystem
0000000
0
0000000
0 resetsystem
00000
0 resetsystem
reset
resetsystem
reset
resetsystem
reset
0
resetsystem
IN
Table 16-7: RegAcCfg3
Table 16-8: RegAcCfg4
Table 16-9: RegAcCfg5
and V
16-4
REF
, the input voltage is modulated and amplified through
S
description
description
description
much higher than the input signal's Nyquist rate (typically f
Input channel configuration selector
Selects default configuration
PGA3 stage offset selection
Reference channel selector
PGA1 stage gain selection
PGA3 stage gain selection
Activity flag
Unused
XE8805/05A
www.semtech.com
S
is 20-