QADC64E Enhanced Mode Operation
MPC561/MPC563 Reference Manual, Rev. 1.2
Freescale Semiconductor
14-71
Figure 14-50. Electrical Model of an A/D Input Signal
, R
F
, R
SRC
and C
F
comprise the external filter circuit. C
P
is the internal parasitic capacitor.
C
SAMP
is the capacitor array used to sample and hold the input voltage. V
I
is an internal voltage source used
to provide charge to C
SAMP
during sample phase.
The following paragraphs provide a simplified description of the interaction between the QADC64E and
the external circuitry. This circuitry is assumed to be a simple RC low-pass filter passing a signal from a
source to the QADC64E input signal. The following simplifying assumptions are made:
•
The external capacitor is perfect (no leakage, no significant dielectric absorption characteristics,
etc.)
•
All parasitic capacitance associated with the input signal is included in the value of the external
capacitor
•
Inductance is ignored
•
The “on” resistance of the internal switches is 0
Ω
and the “off” resistance is infinite
14.6.5.1
Analog Input Considerations
The source impedance of the analog signal to be measured and any intermediate filtering should be
considered whether external multiplexing is used or not.
shows the connection of eight
typical analog signal sources to one QADC64E analog input signal through a separate multiplexer chip.
Also, an example of an analog signal source connected directly to a QADC64E analog input channel is
displayed.
QADC64E Sample AMP Model
S1
AMP
RF
S3
S2
C
SAMP
V
I
C
P
C
F
V
SRC
Internal Circuit Model
External Filter
= Source Voltage
= Internal Parasitic Capacitance
V
SRC
R
F
C
F
C
P
C
SAMP
= Sample Capacitor
V
I
= Filter Impedance
= Filter Capacitor
= Internal Voltage Source During Sample and Hold
Source
R
SRC
R
SRC
= Source Impedance
Summary of Contents for MPC561
Page 84: ...MPC561 MPC563 Reference Manual Rev 1 2 lxxxiv Freescale Semiconductor...
Page 144: ...Signal Descriptions MPC561 MPC563 Reference Manual Rev 1 2 2 46 Freescale Semiconductor...
Page 206: ...Central Processing Unit MPC561 MPC563 Reference Manual Rev 1 2 3 62 Freescale Semiconductor...
Page 302: ...Reset MPC561 MPC563 Reference Manual Rev 1 2 7 14 Freescale Semiconductor...
Page 854: ...Time Processor Unit 3 MPC561 MPC563 Reference Manual Rev 1 2 19 24 Freescale Semiconductor...
Page 968: ...Development Support MPC561 MPC563 Reference Manual Rev 1 2 23 54 Freescale Semiconductor...
Page 1144: ...Internal Memory Map MPC561 MPC563 Reference Manual Rev 1 2 B 34 Freescale Semiconductor...
Page 1212: ...TPU3 ROM Functions MPC561 MPC563 Reference Manual Rev 1 2 D 60 Freescale Semiconductor...
Page 1216: ...Memory Access Timing MPC561 MPC563 Reference Manual Rev 1 2 E 4 Freescale Semiconductor...