AN1740 Freescale Semiconductor / Motorola, AN1740 Datasheet - Page 16

• Manufacturer Part Number: AN1740
• Description: Applications Using the Analog Subsystem on MC68HC05JJ/JP Series Microcontrollers
• Manufacturer: Freescale Semiconductor / Motorola

Application Note
Comparator
Inversion
16
A — INITIAL INPUT OFFSET POSITIVE
V
P
= V
TRIPS WHEN BOTH
INPUTS EQUAL
N
+ V
V
IO
N
+
–
+
IN BOTH CASES, THE OUTPUT (X) RISES WHEN THE (+) INPUT RISES ABOVE THE (–) INPUT.
V
inputs may be within the common mode range above V
offset voltage of a comparator can be modeled as a small internal
voltage source in series with either input of a voltage comparator as
shown in
In case A, the small V
comparator. If both inputs to the comparator are to be equal, then the
applied positive input must rise an additional amount equal to V
the comparator trip condition occurs when:
In case B, the small V
comparator. If both inputs to the comparator are to be equal, then the
applied positive input must fall an additional amount equal to V
the comparator trip condition occurs when:
If the input offset can be moved between the inputs, then the sign of its
contribution to V
actually the result of silicon device sizes and their matching, it cannot
actually “move” between inputs. But the sense of the inputs can be
redefined by interchanging what the inputs to the comparator are called
while also inverting the comparator’s output sense as shown in
8. In these cases, the actual offset stays with the same internal
IO
Figure 7. Comparator Input Offset Model
–
Freescale Semiconductor, Inc.
For More Information On This Product,
+
–
Figure
IDEAL
COMPARATOR
Go to: www.freescale.com
P
X
7.
can effectively change. Since the input offset is
IO
IO
source is in series with the negative input of the
source is in series with the positive input of the
V
V
V
P
P
P
= V
= V
= V
N
TRIPS WHEN BOTH
INPUTS EQUAL
– V
B — INITIAL INPUT OFFSET NEGATIVE
IO
N
N
V
N
+ V
– V
+
–
IO
IO
+
V
IO
–
+
–
SS
IDEAL
COMPARATOR
. The input
MOTOROLA
IO
IO
X
Figure
. Thus,
. Thus,
AN1740