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CY8C28xxx PSoC Programmable System-on-Chip TRM, Document No. 001-52594 Rev. *G
Two Column Limited Analog System
24.1.4
Analog Reference
The PSoC device is a single supply part, with no negative
voltage available or applicable. The limited analog columns
in CY8C28xxx PSoC devices support only one analog refer-
ence, which is the bandgap voltage VBG. This voltage is
routed to the CT blocks in each analog column. VBG is
available at both positive and negative inputs of each CT
amplifier.
DAC functions are relative to the power supply range (Vss to
Vdd). The bandgap VBG reference can be used to calibrate
the supply range. Single slope ADC operation relies on a
calibration step, using the internal bandgap reference or
other user-supplied reference. If the bandgap reference is
used, the ADC gives absolute voltage conversions.
For CT amplifiers configured as comparators (that is, open
loop), a selected analog pin can be compared against
another pin (fed from the other block), VBG, or a supply-ref-
erenced DAC voltage from the SC integrator. With the ana-
log multiplexer bus in the CY8C28xxx PSoC devices, a Port
0 pin can be compared against another pin without using
resources of the adjacent column.
24.1.5
Continuous Time PSoC Block
The CY8C28xxx Continuous Time blocks (Type ACE) are
built around a low power, low offset amplifier. The CT block
can be configured in two modes: As a unity gain buffer to
drive to the other column or open loop as a comparator.
To configure as a comparator, select any NMux choice
except feedback (FB). To enable the comparator bus output,
the CompBus signal must be set in the ACE0xCR1 register.
See
.
There are two discrete outputs from this block. These out-
puts connect to the following buses:
1. The comparator bus (CBUS), which is a digital bus that
is a resource shared by all of the analog blocks in a col-
umn for that block. This output is available to system
interface logic.
2. The local output bus (OUT), which is routed to the neigh-
boring block.
Figure 24-10. Analog Continuous Time Block Diagram
24.1.6
Switched Capacitor PSoC Block
The analog switched capacitor blocks accept a bit stream
from either a digital block or a CT comparator. The SC block
integrates this input and its output can then be connected to
a CT block.
The low power SC block (Type ASE) is automatically
enabled whenever the CT block is powered up. Refer to the
ACE0xCR2 register definition in this chapter.
Figure 24-11. Analog Switch Capacitor PSoC Bloc
24.1.6.1
Application Description for the SC
Block
The Analog Switched Capacitor (SC) blocks support DACs
for comparator references. This application requires the use
of one CT block. Analog-to-digital conversions can be done
with a firmware-based successive approximation algorithm,
using the SC block to provide a DAC reference.
The integrator speed can be modified to trade off accuracy
for settling time.
24.2
PSoC Device Distinctions
The following are PSoC device distinctions for the
CY8C28xxx PSoC devices.
Block Inputs
PMux
CBUS
NMux
Block Inputs
FB
Port Inputs
VBG
OUT
-
+
CompBus
Analog Mux Bus 1
VBG
Analog Mux Bus 0
Swtiched Capacitor
CT Comp Bus
To CT
Block
Digital Blocks
Integrator
Содержание CY8C28 series
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