max5888egktd Maxim Integrated Products, Inc., max5888egktd Datasheet - Page 14

• Manufacturer Part Number: max5888egktd
• Description: Max5888 3.3v, 16-bit, 500msps High Dynamic Performance Dac With Differential Lvds Inputs
• Manufacturer: Maxim Integrated Products, Inc.

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 transmitter
operates with four/eight in-band carriers, each individ-
ual 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.
Other key factors in selecting the appropriate DAC for
the Tx path of a multicarrier GSM/EDGE system is the
converter’s ability to offer superior IMD and MTPR perfor-
mance. Multiple carriers in a designated band generate
unwanted intermodulation distortion between the individ-
ual carrier frequencies. A multitone test vector usually
consists of several equally spaced carriers, usually four,
with identical amplitudes. Each of these carriers is rep-
resentative of a channel within the defined bandwidth of
interest. To verify MTPR, one or more tones are
removed such that the intermodulation distortion perfor-
3.3V, 16-Bit, 500Msps High Dynamic
Performance DAC with Differential LVDS Inputs
Table 3. Summary of Important AC Performance Parameters for Multicarrier GSM/EDGE
Systems
*Measured within a 25MHz window.
14
SFDR
SNR
IMD
Carrier Amplitude
______________________________________________________________________________________
SNR
SPECIFICATION
MIN
= -80dBc - 10
SNR
MIN
= -130dBc/Hz
✕
log
SYSTEM TRANSMITTER
10
OUTPUT LEVELS
(100
-130dBc/Hz
-70dBc
80dBc
N/S
✕
10
3
Hz)
DAC REQUIREMENTS WITH
mance of the DAC can be evaluated. Nonlinearities
associated with the DAC create spurious tones, some
of which may fall back into the area of the removed
tone, limiting a channel’s carrier-to-noise ratio. Other
spurious components falling outside the band of inter-
est can also be important, depending on the system’s
spectral mask and filtering requirements. Going back to
the GSM/EDGE Tx mask, the IMD specification for adja-
cent carriers varies somewhat among the different GSM
standards. For the PCS1800 and GSM850 standards,
the DAC must meet an average IMD of -70dBc.
Table 3 summarizes the dynamic performance require-
ments for the entire Tx signal chain in a four-carrier
GSM/EDGE-based system and compares the previous-
ly established converter requirements with a new-gen-
eration high dynamic performance DAC.
The four-tone MTPR plot in Figure 12 demonstrates the
MAX5888’s excellent dynamic performance. The center
frequency (f
allow detection and analysis of intermodulation or spuri-
ous components falling back into this empty spot from
adjacent channels. The four carriers are observed over
a 12MHz bandwidth and are equally spaced at 1MHz.
Each individual output amplitude is backed off to -12dB
FS. Under these conditions, the DAC yields an MTPR
performance of -78dBc.
Table 2. GSM/EDGE Noise Requirements
for Multicarrier Systems
NUMBER OF
CARRIERS
-152dB FS/Hz
2
4
8
MARGINS
-12dB FS
-75dBc
86dBc
CENTER
POWER LEVEL
CARRIER
(dB FS)
= 31.97MHz) has been removed to
-12
-18
-6
MAX5888 SPECIFICATIONS
DAC NOISE DENSITY
REQUIREMENT
-165dB/Hz
-12dB FS
82dBc*
-78dBc
(dB FS/Hz)
-152
-158
-146