MAX1185_10 Datasheet, PDF(13/21 Page) Maxim Integrated Products – Dual 10-Bit, 20Msps, 3V, Low-Power ADC with Internal Reference and Multiplexed Parallel Outputs

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MAX1185_10 Datasheet, PDF (13/21 Pages) Maxim Integrated Products – Dual 10-Bit, 20Msps, 3V, Low-Power ADC with Internal Reference and Multiplexed Parallel Outputs

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Dual 10-Bit, 20Msps, 3V, Low-Power ADC with

Internal Reference and Multiplexed Parallel Outputs

5 CLOCK-CYCLE LATENCY (CHA), 5.5 CLOCK-CYCLE LATENCY (CHB)

CHA

CHB

tCLK

tCL

tCH

CLK

tDOB

tDOA

A/B

CHB

CHA

CHB

CHA

CHB

CHA

CHB

CHA

CHB

CHA

CHB

CHA

CHB

tDA/B

D0A/B-D9A/B D0B

D1A

D1B

D2A

D2B

D3A

D3B

D4A

D4B

D5A

D5B

D6A

D6B

Figure 3. Timing Diagram for Multiplexed Outputs

tENABLE

OUTPUT HIGH IMPEDANCE

D0A/BâD9A/B

tDISABLE

VALID DATA

HIGH

IMPEDANCE

Figure 4. Output Timing Diagram

Applications Information

Figure 5 depicts a typical application circuit containing

two single-ended to differential converters. The internal

reference provides a VDD / 2 output voltage for level

shifting purposes. The input is buffered and then split

to a voltage follower and inverter. One lowpass filter per

ADC suppresses some of the wideband noise associat-

ed with high-speed operational amplifiers that follows

the amplifiers. The user may select the RISO and CIN

values to optimize the filter performance, to suit a par-

ticular application. For the application in Figure 5, a

RISO of 50â¦ is placed before the capacitive load to

prevent ringing and oscillation. The 22pF CIN capacitor

acts as a small bypassing capacitor.

Using Transformer Coupling

An RF transformer (Figure 6) provides an excellent

solution to convert a single-ended source signal to a

fully differential signal, required by the MAX1185 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 may be selected to reduce the drive

requirements. A reduced signal swing from the input

driver, such as an op amp, may also improve the over-

all distortion.

In general, the MAX1185 provides better SFDR and

THD with fully differential input signals than single-

ended drive, especially for very high input frequencies.

In differential input mode, even-order harmonics are

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

balanced, and each of the ADC inputs only requires

half the signal swing compared to single-ended mode.

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