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MAX5886

3.3V, 12-Bit, 500Msps High Dynamic

Performance DAC with Differential LVDS Inputs

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between the frequency components located within the

carrier band. The energy at one end of the carrier band

generates IM products with the energy from the oppo-

site end of the carrier band. For single-carrier W-CDMA

modulation, these IMD products are spread 3.84MHz

over the adjacent sideband. Four contiguous W-CDMA

carriers spread their IM products over a bandwidth of

20MHz on either side of the 20MHz total carrier band-

width. In this four-carrier scenario, only the energy in

the first adjacent 3.84MHz side band is considered for

ACLR 1. To measure ACLR, drive the converter with a

W-CDMA pattern. Make sure that the signal is backed

off by the peak-to-average ratio, such that the DAC is

not clipping the signal. ACLR can then be measured

with the ACLR measurement function built into your

spectrum analyzer.

Figure 9 shows the ACLR performance for a single

W-CDMA carrier (f

CLK

= 184.32MHz, f

OUT

= 61.44MHz)

applied to the MAX5886 (including measurement sys-

tem limitations*).

Figure 10 illustrates the ACLR test results for the

MAX5886 with a four-carrier W-CDMA signal at an out-

put frequency of 63.98MHz and sampling frequency of

184.32MHz. Considerable care must be taken to

ensure accurate measurement of this parameter.

Multitone Testing for GSM/EDGE

Applications

The transmitter sections of multicarrier base station

transceiver systems for GSM/EDGE usually present

communication DAC manufacturers with the difficult

task of providing devices with higher resolution, while

simultaneously reducing noise and spurious emissions

over a desired bandwidth.

To specify noise and spurious emissions from base sta-

tions, a GSM/EDGE Tx mask is used to identify the DAC

requirements for these parameters. This mask shows

that the allowable levels for noise and spurious emis-

sions are dependent on the offset frequency from the

transmitted carrier frequency. The GSM/EDGE mask

and its specifications are based on a single active car-

rier with any other carriers in the transmitter being dis-

abled. Specifications displayed in Figure 11 support

per-carrier output power levels of 20W or greater.

Lower output power levels yield less-stringent emission

requirements. For GSM/EDGE applications, the DAC

demands spurious emission levels of less than -80dBc

for offset frequencies ≥6MHz. Spurious products from

the DAC can combine with both random noise and spu-

rious products from other circuit elements. The spuri-

ous products from the DAC should therefore be backed

off by 6dB or more to allow for these other sources and

still avoid signal clipping.

The number of carriers and their signal levels with

respect to the full scale of the DAC are important as

well. Unlike a full-scale sine wave, the inherent nature

of a multitone signal contains higher peak-to-RMS

ratios, raising the prospect for potential clipping, if the

signal level is not backed off appropriately. If a trans-

mitter operates with four/eight in-band carriers, each

*Note that due to their own IM effects and noise limitations, spectrum analyzers introduce ACLR errors, which can falsify the measure-

ment. For a single-carrier ACLR measurement greater than 70dB, these measurement limitations are significant, becoming even more

restricting for multicarrier measurement. Before attempting an ACLR measurement, it is recommended consulting application notes pro-

vided by major spectrum analyzer manufacturers that provide useful tips on how to use their instruments for such tests.

-145

-110

-130

-120

-140

-100

-90

-80

-70

-60

-50

-30

-40

ANALOG OUTPUT POWER (dBm)

-25

3.5MHz/div

CENTER

= 61.44MHz

CLK

= 184.32Mbps

ACLR = 70dB

Figure 9. ACLR for W-CDMA Modulation, Single Carrier