channel when using the MAX158/MX7828 and 100kHz

per channel when using the MAX154/MX7824. These

rates are well above the Nyquist requirement of 20kHz

sampling rate for a 10kHz input bandwidth.

Bipolar Input Operation

The circuit in Figure 10a can be used for bipolar input

operation. The input voltage is scaled by an amplifier so

that only positive voltages appear at the ADC’s inputs.

An external reference should be used for the MX7824/

MX7828, but is not needed with the MAX154/MAX158.

The analog input range is ±4V and the output code is

complementary offset binary. The ideal input/output

characteristic is shown in Figure 10b.

CMOS, High-Speed, 8-Bit ADCs

with Multiplexer

10

______________________________________________________________________________________

1pF

12pF

2pF

1pF

•

•

•

15 LSB COMPARATORS

TO LS

LADDER

1pF

1pF

•

•

•

16 MSB COMPARATORS

TO MS

LADDER

AIN1

11111111

11111110

10000010

10000001

01111111

01111110

10000000

00000001

00000000

00000010

0V

AIN INPUT VOLTAGE (LSBs)

FS = 8V

1LSB = FS / 256

11111101

+FS

2

-FS + 1LSB

2

AIN1

2pF

2pF

32pF

B MUX

600

Ω

350

Ω

MAX154

MAX158

AIN1

ONLY CHANNEL 1 SHOWN

REF OUT

GND

11.5

Ω

3.57k

10.0k

0.01

µF

0.01

µF

0.1

µF

47

µF

16.2k

+5V

CS

RDY

INT

DB0–DB7

RD

Figure 9a. Equivalent Input Circuit

Figure 10b. Transfer Function for ±4V Input Operation

Figure 9b. RC Network Model

Figure 10a. Bipolar ±4V Input Operation