Datasheet
MAX5884
3.3V, 14-Bit, 200Msps High Dynamic
Performance DAC with CMOS Inputs
14 ______________________________________________________________________________________
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-
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 11 demonstrates the
MAX5884’s excellent dynamic performance. The center
frequency (f
CENTER
= 31.99MHz) has been removed to
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 -82dBc.
Grounding, Bypassing, and Power-Supply
Considerations
Grounding and power-supply decoupling can strongly
influence the performance of the MAX5884. Unwanted
digital crosstalk may couple through the input, refer-
ence, power supply, and ground connections, affecting
dynamic performance. Proper grounding and power-
supply decoupling guidelines for high-speed, high-fre-
quency applications should be closely followed. This
reduces EMI and internal crosstalk that can significantly
affect the dynamic performance of the MAX5884.
Use of a multilayer printed circuit (PC) board with sepa-
rate ground and power-supply planes is recommend-
ed. High-speed signals should run on lines directly
above the ground plane. Since the MAX5884 has sepa-
rate analog and digital ground buses (AGND,
CLKGND, and DGND, respectively), the PC board
should also have separate analog and digital ground
sections with only one point connecting the two planes.
Digital signals should be run above the digital ground
plane and analog/clock signals above the analog/clock
ground plane. Digital signals should be kept as far
away from sensitive analog inputs, reference input
sense lines, common-mode input, and clock inputs as
practical. A symmetric design of clock input and analog
output lines is recommended to minimize 2nd-order
NUMBER OF
CARRIERS
CARRIER
POWER LEVEL
(dB FS)
DAC NOISE DENSITY
REQUIREMENT
(dB FS/Hz)
2 -6 -146
4 -12 -152
Table 2. GSM/EDGE Noise Requirements
for Multicarrier Systems
SPECIFICATION
SYSTEM TRANSMITTER
OUTPUT LEVELS
DAC REQUIREMENTS WITH
MARGINS
MAX5884 SPECIFICATIONS
SFDR 80dBc 86dBc 76dBc*
Noise Spectral Density -130dBc/Hz -152dB FS/Hz -153dB FS/Hz
IMD -70dBc -75dBc -74dBc
Carrier Amplitude N/S -12dB FS -12dB FS
Table 3. Summary of Important AC Performance Parameters for Multicarrier GSM/EDGE
Systems
*Measured within a 15MHz window.