MAX1192 datasheet(21/28 Pages) MAXIM

21 / 28 page

Ultra-Low-Power, 22Msps, Dual 8-Bit ADC

______________________________________________________________________________________

Using Transformer Coupling

An RF transformer (Figure 8) provides an excellent

solution to convert a single-ended source signal to a

fully differential signal, required by the MAX1192 for

optimum performance. Connecting the center tap of the

transformer to COM provides a VDD/2 DC level shift to

the input. Although a 1:1 transformer is shown, a 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.

In general, the MAX1192 provides better SFDR and

THD with fully differential input signals than single-

ended drive, especially for high input frequencies. In

differential input mode, even-order harmonics are lower

as both inputs (INA+, INA- and/or INB+, INB-) are bal-

anced, and each of the ADC inputs only requires half

the signal swing compared to single-ended mode.

Single-Ended AC-Coupled Input Signal

Figure 9 shows an AC-coupled, single-ended applica-

tion. Amplifiers such as the MAX4108 provide high

speed, high bandwidth, low noise, and low distortion to

maintain the input signal integrity.

Buffered External Reference Drives

Multiple ADCs

The buffered external reference mode allows for more

control over the MAX1192 reference voltage and allows

multiple converters to use a common reference. To

drive one MAX1192 in buffered external reference

mode, the external circuit must sink 0.7µA, allowing one

reference circuit to easily drive the REFIN of multiple

converters to 1.024V ±10%.

MAX1192

N.C.

VIN

22pF

0.1

µF

0.1

µF

2.2

µF

Ω

MINICIRCUITS

TT1-6-KK81

N.C.

VIN

22pF

0.1

µF

0.1

µF

2.2

µF

Ω

MINICIRCUITS

TT1-6-KK81

INA-

INA+

INB-

INB+

COM

Figure 8. Transformer-Coupled Input Drive

MAX1192

0.1

µF

Ω

100

Ω

100

Ω

CIN

22pF

CIN

22pF

INB+

INB-

COM

INA+

INA-

0.1

µF

RISO

Ω

RISO

Ω

REFP

REFN

VIN

MAX4108

0.1

µF

Ω

100

Ω

100

Ω

CIN

22pF

CIN

22pF

0.1

µF

RISO

Ω

RISO

Ω

REFP

REFN

VIN

MAX4108

Figure 9. Using an Op Amp for Single-Ended, AC-Coupled

Input Drive

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