max5884egmtd Maxim Integrated Products, Inc., max5884egmtd Datasheet - Page 13

• Manufacturer Part Number: max5884egmtd
• Description: Max5884 3.3v, 14-bit, 200msps High Dynamic Performance Dac With Cmos Inputs
• Manufacturer: Maxim Integrated Products, Inc.

Figure 9. ACLR for W-CDMA Modulation, Four Carriers
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 10 support
per-carrier output power levels of 20W or greater.
Lower output power levels yield less stringent emission
requirements.
Figure 8. ACLR for W-CDMA Modulation, Single Carrier
-100
-110
-120
-100
-110
-120
-20
-30
-40
-50
-60
-70
-80
-90
-20
-30
-40
-60
-70
-80
-90
-50
Multitone Testing for GSM/EDGE
______________________________________________________________________________________
f
CLK
= 184.32MHz, f
Performance DAC with CMOS Inputs
4MHz/div
4MHz/div
3.3V, 14-Bit, 200Msps High Dynamic
f
CENTER
CENTER
f
CLK
ACLR = 68dB
= 184.32MHz
ACLR = 72dB
= 30.72MHz
= 30.72MHz
Applications
For GSM/EDGE applications, the DAC demands spuri-
ous emission levels of less than -80dBc for offset fre-
quencies ≥6MHz. Spurious products from the DAC can
combine with both random noise and spurious prod-
ucts from other circuit elements. The spurious products
from the DAC should therefore be backed off by 6dB or
more to allow for these other sources and still avoid sig-
nal 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
individual carrier must be operated at less than
-12dB FS/-18dB FS to avoid waveform clipping.
The noise density requirements (Table 2) for a
GSM/EDGE-based system can again be derived from
the system’s Tx mask. With a worst-case noise level of
-80dBc at frequency offsets of ≥6MHz and a measure-
ment bandwidth of 100kHz, the minimum noise density
per hertz is calculated as follows:
Since random DAC noise adds to both the spurious tones
and to random noise from other circuit elements, it is rec-
ommended reducing the specification limits by about
10dB to allow for these additional noise contributions
while maintaining compliance with the Tx mask values.
Figure 10. GSM/EDGE Tx Mask Requirements
-30
-60
-70
-73
-75
-80
-90
O
SNR
0.2 0.4 0.6
MIN
= -80dBc - 10
SNR
FREQUENCY OFFSET FROM CARRIER (MHz)
MEASUREMENT BANDWIDTH
MIN
1.2
30kHz 100kHz
= -130dBc/Hz
1.8
✕
log
10
6.0
IMD REQUIREMENT: < -70dBc
(100
INBAND
✕
OUTBAND
10
3
WORST-CASE
NOISE LEVEL
Hz)
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