MOTOROLA
Chapter 27. Queued Analog-to-Digital Converter (QADC)
27-63
Signal Connection Considerations
27.9.1 Analog Reference Signals
No A/D converter can be more accurate than its analog reference. Any noise in the
reference can result in at least that much error in a conversion. The reference for the QADC,
supplied by signals V
RH
and V
RL
, should be low-pass filtered from its source to obtain a
noise-free, clean signal. In many cases, simple capacitive bypassing may suffice. In
extreme cases, inductors or ferrite beads may be necessary if noise or RF energy is present.
External resistance may introduce error in this architecture under certain conditions. Any
series devices in the filter network should contain a minimum amount of DC resistance.
For accurate conversion results, the analog reference voltages must be within the limits
defined by V
DDA
and V
SSA
, as explained in this subsection.
27.9.2 Analog Power Signals
The analog supply signals (V
DDA
and V
SSA
) define the limits of the analog reference
voltages (V
RH
and V
RL
) and of the analog multiplexer inputs. Figure 27-44 is a diagram of
the analog input circuitry.
Figure 27-44. Equivalent Analog Input Circuitry
Because the sample amplifier is powered by V
DDA
and V
SSA
, it can accurately transfer
input signal levels up to but not exceeding V
DDA
and down to but not below V
SSA.
If the
input signal is outside of this range, the output from the sample amplifier is clipped.
In addition, V
RH
and V
RL
must be within the range defined by V
DDA
and V
SSA
. As long as
V
RH
is less than or equal to V
DDA
, and V
RL
is greater than or equal to V
SSA
, and the sample
amplifier has accurately transferred the input signal, resolution is ratiometric within the
limits defined by V
RL
and V
RH
. If V
RH
is greater than V
DDA
, the sample amplifier can
Sample
AMP
16 Channels Total
V
RL
V
DDA
V
RH
S/H
Comparator
C
V
SSA
Summary of Contents for ColdFire MCF5281
Page 124: ...3 20 MCF5282 User s Manual MOTOROLA EMAC Instruction Set Summary ...
Page 141: ...MOTOROLA Chapter 5 Static RAM SRAM 5 5 SRAM Programming Model ...
Page 142: ...5 6 MCF5282 User s Manual MOTOROLA SRAM Programming Model ...
Page 168: ...6 26 MCF5282 User s Manual MOTOROLA Interrupts ...
Page 186: ...7 18 MCF5282 User s Manual MOTOROLA Functional Description ...
Page 228: ...9 22 MCF5282 User s Manual MOTOROLA Functional Description ...
Page 246: ...10 18 MCF5282 User s Manual MOTOROLA Low Power Wakeup Operation ...
Page 254: ...11 8 MCF5282 User s Manual MOTOROLA Memory Map and Registers ...
Page 264: ...12 10 MCF5282 User s Manual MOTOROLA Chip Select Registers ...
Page 280: ...13 16 MCF5282 User s Manual MOTOROLA Misaligned Operands ...
Page 314: ...14 34 MCF5282 User s Manual MOTOROLA MCF5282 External Signals ...
Page 339: ...MOTOROLA Chapter 15 Synchronous DRAM Controller Module 15 25 SDRAM Example ...
Page 340: ...15 26 MCF5282 User s Manual MOTOROLA SDRAM Example ...
Page 356: ...16 16 MCF5282 User s Manual MOTOROLA DMA Controller Module Functional Description ...
Page 408: ...17 52 MCF5282 User s Manual MOTOROLA Buffer Descriptors ...
Page 446: ...20 24 MCF5282 User s Manual MOTOROLA Interrupts ...
Page 474: ...22 18 MCF5282 User s Manual MOTOROLA Programming Model ...
Page 510: ...23 36 MCF5282 User s Manual MOTOROLA Operation ...
Page 526: ...24 16 MCF5282 User s Manual MOTOROLA I2C Programming Examples ...
Page 672: ...28 12 MCF5282 User s Manual MOTOROLA Functional Description ...
Page 718: ...29 46 MCF5282 User s Manual MOTOROLA Motorola Recommended BDM Pinout ...
Page 750: ...32 8 MCF5282 User s Manual MOTOROLA Ordering Information ...