Rainbow Electronics ATmega128L - Manual (Page 221)

221
ATmega128(L)
2467B–09/01
Analog to Digital
Converter
Features •
10-bit Resolution
•
0.5 LSB Integral Non-linearity
• ±2 LSB Absolute Accuracy
•
TBD - 260 µs Conversion Time
•
Up to TBD kSPS at Maximum Resolution
•
8 Multiplexed Single Ended Input Channels
•
7 Differential Input Channels
•
2 Differential Input Channels with Optional Gain of 10x and 200x
•
Optional Left Adjustment for ADC Result Readout
•
0 - VCC ADC Input Voltage Range
•
Selectable 2.56 V ADC Reference Voltage
•
Free Running or Single Conversion Mode
•
Interrupt on ADC Conversion Complete
•
Sleep Mode Noise Canceler
The ATmega128 features a 10-bit successive approximation ADC. The ADC is con-
nected to an 8-channel Analog Multiplexer which allows 8 single-ended voltage inputs
constructed from the pins of Port F. The single-ended voltage inputs refer to 0 V (GND).
The device also supports 16 differential voltage input combinations. Two of the differen-
tial inputs (ADC1, ADC0 and ADC3, ADC2) are equipped with a programmable gain
stage, providing amplification steps of 0 dB (1x), 20 dB (10x), or 46 dB (200x) on the dif-
ferential input voltage before the A/D conversion. Seven differential analog input
channels share a common negative terminal (ADC1), while any other ADC input can be
selected as the positive input terminal. If 1x or 10x gain is used, 8-bit resolution can be
expected. If 200x gain is used, 7-bit resolution can be expected.
The ADC contains a Sample and Hold circuit which ensures that the input voltage to the
ADC is held at a constant level during conversion. A block diagram of the ADC is shown
in
Figure 107.
The ADC has a separate analog supply voltage pin, AVCC. AVCC must not differ more
than
±0.3 V from V
CC
. See the paragraph “ADC Noise Canceler” on page 227 on how to
connect this pin.
Internal reference voltages of nominally 2.56 V or AV
CC
are provided on-chip. The volt-
age reference may be externally decoupled at the AREF pin by a capacitor for better
noise performance.