Rainbow-electronics MAX1208 Bedienungsanleitung PDF herunterladen (Seite 21)

step-up transformer can be selected to reduce the

drive requirements. A reduced signal swing from the

input driver, such as an op amp, can also improve the

overall distortion. The configuration of Figure 10 is good

for frequencies up to Nyquist (f

CLK

/ 2).

The circuit of Figure 11 converts a single-ended input

signal to fully differential just as Figure 10. However,

Figure 11 utilizes an additional transformer to improve

the common-mode rejection, allowing high-frequency

signals beyond the Nyquist frequency. The two sets of

termination resistors provide an equivalent 75Ω termi-

nation to the signal source. The second set of termina-

tion resistors connects to COM, providing the correct

input common-mode voltage. Two 0Ω resistors in series

with the analog inputs allow high IF input frequencies.

These 0Ω resistors can be replaced with low-value

resistors to limit the input bandwidth.

Single-Ended AC-Coupled Input Signal

Figure 12 shows an AC-coupled, single-ended input

application. The MAX4108 provides high speed, high

bandwidth, low noise, and low distortion to maintain the

input signal integrity.

MAX1208

12-Bit, 80Msps, 3.3V ADC

______________________________________________________________________________________ 21

MAX1208

N.C. N.C.

MINICIRCUITS

ADT1-1WT

N.C.

0.1

MINICIRCUITS

ADT1-1WT

Ω

5.6pF

2.2

INP

COM

INN

110

Ω

0.1%

110

Ω

0.1%

Ω

0.5%

Ω

0.5%

Ω

RESISTORS CAN BE REPLACED WITH LOW-VALUE

RESISTORS TO LIMIT THE INPUT BANDWIDTH.

Figure 11. Transformer-Coupled Input Drive for Input Frequencies Beyond Nyquist

MAX1208

N.C.

0.1µF

MINICIRCUITS

TT1-6 OR T1-1T

24.9Ω

12pF

2.2µF

INP

COM

INN

Figure 10. Transformer-Coupled Input Drive for Input

Frequencies Up to Nyquist

MAX1208

5.6pF

2.2µF

INP

COM

INN

24.9Ω

100Ω

0.1µF

MAX4108

Figure 12. Single-Ended, AC-Coupled Input Drive

1 2 ... 16 17 18 19 20 21 22 23 24 25 26 27

12-Bit, 80Msps, 3.3V ADC 1

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