Analog PSoC Blocks
September 5, 2002
Document #: 38-12010 CY Rev. ** CMS Rev. 3.20
73
10.4 Analog Reference and Bias
Control
The references in the analog array are driven by single
op-amps. A single ground referred signal is taken as the
reference input and then offset with respect to analog
ground. The reference can be input on a pin, it can be
taken from the bandgap, or it can be set to be the sup-
plies. A series of op-amps are used to do the level shift-
ing and buffering for driving the array. As more loads are
added on the reference lines, the response will slow
down. Settling time will be roughly linear with load.
A separate bias circuit controls the 3 rows. The first row
is to be controlled independently. The second and third
rows have their bias control tied together.
10.5 AGND, REFHI, REFLO
BGT Bandgap Test is used for internal reference voltage
testing.
HBE controls the bias level. There is a trade-off in the
usage of this bias level. At high bias levels, the op-amp
swings are more limited but the op-amp can be faster. At
low bias levels, wider swings (and hence lower supply
voltages) are possible, but the op-amp is slower.
REF denotes Analog Array Reference Control.
PWR denotes Analog Array Power Control.
Analog Reference Control Register (ARF_CR, Address = Bank 0, 63h)
Table 62:
Analog Reference Control Register
Bit #
7
6
5
4
3
2
1
0
POR
0
0
0
0
0
0
0
0
Read/Write
RW
RW
RW
RW
RW
RW
RW
RW
Bit Name
BGT
HBE
REF[2]
REF[1]
REF[0]
PWR[2]
PWR[1]
PWR[0]
Bit 7
: BGT Bandgap Test used for internal reference voltage testing (customer should not alter; must be written as 0)
Bit 6
: HBE Bias level control for op-amps
0 = Low bias mode for analog array
1 = High bias mode for analog array
Bit [5:3]
: REF [2:0] Analog Array Reference Control
AGND
High/Low
0 0 0 = Vcc/2
± Bandgap
0 0 1 = P2[4]
± P2[6]
0 1 0 = Vcc/2
± Vcc/2
0 1 1 = 2 Bandgap ± Bandgap
1 0 0 = 2 Bandgap ± P2[6]
1 0 1 = P2[4]
± Bandgap
1 1 0 = Reserved
1 1 1 = Reserved
Bit [2:0]
: PWR [2:0] Analog Array Power Control
0 0 0 = All Analog Off
0 0 1 = SC Off, REFPWR Low
0 1 0 = SC Off, REFPWR Med
0 1 1 = SC Off, REFPWR High
1 0 0 = SC On, REFPWR Off
1 0 1 = SC On, REFPWR Low
1 1 0 = SC On, REFPWR Med
1 1 1 = SC On, REFPWR High
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