ATmega128 datasheet(230/386 Pages) ATMEL

230 / 386 page

230

2467S–AVR–07/09

ATmega128

Analog to

Digital

Converter

Features

• 10-bit Resolution

• 0.5 LSB Integral Non-linearity

• ±2 LSB Absolute Accuracy

• 13 - 260 µs Conversion Time

• Up to 76.9 kSPS (Up to 15 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 connected 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 0V (GND).

The device also supports 16 differential voltage input combinations. Two of the differential 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 differential 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 108.

The ADC has a separate analog supply voltage pin, AVCC. AVCC must not differ more than ±

0.3V from V

CC. See the paragraph “ADC Noise Canceler” on page 236 on how to connect this

pin.

Internal reference voltages of nominally 2.56V or AVCC are provided On-chip. The voltage refer-

ence may be externally decoupled at the AREF pin by a capacitor for better noise performance.

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