Rainbow-electronics MAX108 Manual de usuario descargar pdf (Pagina 17)

In a typical single-ended configuration, the analog

input signal (Figure 10a) enters the T/H amplifier stage

at the in-phase input (VIN+), while the inverted phase

input (VIN-) is reverse-terminated to GNDI with an

external 50Ω resistor. Single-ended operation allows for

an input amplitude of ±250mV. Table 3 shows a selec-

tion of input voltages and their corresponding output

codes for single-ended operation.

Differential Analog Inputs

To obtain a full-scale digital output with differential input

drive (Figure 10b), 250mVp-p must be applied between

VIN+ and VIN- (VIN+ = +125mV, and VIN- = -125mV).

Midscale digital output codes (01111111 or 10000000)

occur when there is no voltage difference between

VIN+ and VIN-. For a zero-scale digital output code, the

in-phase (VIN+) input must see -125mV and the invert-

ed input (VIN-) must see +125mV. A differential input

drive is recommended for best performance. Table 4

represents a selection of differential input voltages and

their corresponding output codes.

MAX108

±5V, 1.5Gsps, 8-Bit ADC with

On-Chip 2.2GHz Track/Hold Amplifier

______________________________________________________________________________________ 17

+2.8V

50Ω

VIN+

ANALOG INPUTS ARE ESD PROTECTED

(NOT SHOWN IN THIS SIMPLIFIED DRAWING).

VIN-

GNDI

Figure 9. Simplified Analog Input Structure (Single-Ended/

Differential)

IN+

IN-

+250mV

-250mV

500mVp-p

FS ANALOG

INPUT RANGE

= ±250mV

500mV

Figure 10a. Single-Ended Analog Input Signals

IN+

IN-

+125mV

-125mV

±250mV

FS ANALOG

INPUT RANGE

250mV

-250mV

Figure 10b. Differential Analog Input Signals

Table 3. Ideal Input Voltage and Output Code Results for Single-Ended Operation

0-250mV 00000000 (zero scale)0V

0-250mV + 1LSB 0000001

00V

01111111

toggles

10000000

0+250mV - 1LSB 111111110V

OUTPUT CODEVIN+ OVERRANGE BIT

VIN-

+250mV 11111111 (full scale)0V

1 2 ... 12 13 14 15 16 17 18 19 20 21 22 ... 31 32

±5V, 1.5Gsps, 8-Bit ADC with 1

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Rainbow-electronics MAX108 Manual de usuario Pagina 17

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