AD9789 Analog Devices, AD9789 Datasheet - Page 55

• Manufacturer Part Number: AD9789
• Description: 14-Bit, 2400 MSPS RF DAC with 4-Channel Signal Processing
• Manufacturer: Analog Devices

Specifications of AD9789

• Resolution (bits): 14bit
• Dac Update Rate: 2.4GSPS
• Dac Settling Time: 13ns
• Max Pos Supply (v): +3.47V
• Single-supply: No
• Dac Type: Current Out
• Dac Input Format: LVDS,Par

Switching between analog modes reshapes the sinc roll-off
inherent at the DAC output. The performance and maximum
amplitude in all three Nyquist zones is affected by this sinc
roll-off depending on where the carrier is placed, as shown in
Figure 106.
The RZ mode, with its lower but flat response, can be quite
useful for quick checks of system frequency response.
(
Figure 106. Sinc Roll-Off for Each Analog Operating Mode (f
DAC OUTPUT
f
DAC OUTPUT
(RETURN-TO-
ZERO MODE)
S
INPUT DATA
MIX MODE)
4-SWITCH
4-SWITCH
DACCLK
–10
–15
–20
–25
–30
–35
–5
0
0
Figure 105. Mix Mode and RZ Mode DAC Waveforms
RZ MODE
NYQUIST ZONE
D1
D1
D1
FIRST
–D1
0.5
D2
D2
D2
–D2
D3
D3
D3
–D3
1.0
FREQUENCY (Hz)
D4
D4
NYQUIST ZONE
D4
–D4
SECOND
MIX MODE
D5
D5
1.5
D5
–D5
D6
D6
D6
–D6
NORMAL
MODE
2.0
D7
D7
D7
–D7
NYQUIST ZONE
D8
D8
D8
–D8
THIRD
2.5
D9
D9
S
D9
–D9
= 2 × DACCLK)
D10
D10
D10
–D10
3.0
t
t
Rev. A | Page 55 of 76
ANALOG CONTROL REGISTERS
The AD9789 includes registers for optimizing its analog
performance. These registers include noise reduction in the
output current mirror and output current mirror headroom
adjustments.
Mirror Roll-Off Frequency Control
Using the MSEL[1:0] bits (Register 0x36[1:0]), the user can
adjust the noise contribution of the internal current mirror to
optimize the 1/f noise. Figure 107 shows MSEL vs. the 1/f noise
with 20 mA full-scale current into a 50 Ω resistor.
–110
–115
–120
–125
–130
–135
–140
1
Figure 107. 1/f Noise with Respect to MSEL Bits
FREQUENCY (kHz)
MSEL = 10
10
MSEL = 01
MSEL = 00
MSEL = 11
AD9789
100