Low-Cost, 2-Channel, ±14-Bit Serial ADCs

10

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Oversampling Clock

XCLK internally connects to a clock-frequency divider

network, whose output is the ADC oversampling clock,

oscillator or external clock applied to XCLK) to be

divided by one, two, or four (see

Clock Divider-Ratio

Control Bits).

Figure 3 shows the two methods for providing the over-

sampling clock to the MAX110/MAX111. In external-

clock mode (Figure 3a), the internal RC oscillator is

disabled and XCLK accepts a TTL/CMOS-level clock to

provide the oversampling clock to the ADC.

Select external-clock mode (Figure 3a) by connecting

RCSEL to GND and a TTL/CMOS-compatible clock to

XCLK (see

Selecting the Oversampling Clock

Frequency).

In RC-oscillator mode (Figure 3b), the internal RC oscil-

lator is active and its output is connected to XCLK

(Figure 1). Select RC-oscillator mode by connecting

connects it to XCLK for use by the ADC and external

system components. Minimize the capacitive loading on

XCLK when using the internal RC oscillator.

DIFFERENTIAL

ANALOG

INPUT

OUTPUT FROM

1-BIT DAC

OVERSAMPLING

CLOCK

MAX110

MAX111

Figure 2. ADC Waveforms During a Conversion

Figure 1. Functional Diagram

IN1+

IN+

IN-

INPUT

MUX

IN1-

IN2+

IN2-

REF+

Gm

REF-

Gm

INTEGRATOR

UP/DOWN

COUNTER

-

Σ

∫

DITHER

GENERATOR

SERIAL

SHIFT

REGISTER

DIN

SCLK CS

16

16

16

16

CONTROL

REGISTER

DOUT

BUSY

RCSEL

XCLK

OSC

TIMER + CONTROL

LOGIC + CLOCK GENERATOR

DIVIDER

NETWORK,

DIVIDE BY

1, 2, OR 4

RC

OSCILLATOR

MAX110

MAX111