AD9146 Analog Devices, AD9146 Datasheet - Page 40

• Manufacturer Part Number: AD9146
• Description: Dual, 16-Bit, 1230 MSPS, TxDAC+® Digital-to-Analog Converter
• Manufacturer: Analog Devices

Specifications of AD9146

• Resolution (bits): 16bit
• Dac Update Rate: 1.23GSPS
• Dac Settling Time: n/a
• Max Pos Supply (v): +3.47V
• Single-supply: No
• Dac Type: Current Out
• Dac Input Format: Byte,LVDS,Nibble

AD9146
Figure 52 shows the most basic transmit DAC output circuitry.
A pair of resistors, R
mentary output currents to a differential voltage output, V
Because the current outputs of the DAC are high impedance,
the differential driving point impedance of the DAC outputs,
R
waveforms.
The common-mode signal voltage, V
The peak output voltage, V
With this circuit configuration, the single-ended peak voltage is
the same as the peak differential output voltage.
Transmit DAC Linear Output Signal Swing
To achieve optimum performance, the DAC outputs have a
linear output compliance voltage range that must be adhered
to. The linear output signal swing is dependent on the full-scale
output current, I
Figure 54 shows the IMD performance vs. the output common-
mode voltage at different full-scale currents.
OUT
, is equal to 2 × R
V
V
+V
–V
PEAK
CM
PEAK
PEAK
V
CM
=
= I
0
I
2
Figure 52. Basic Transmit DAC Output Circuit
FS
FS
V
× R
×
N
Figure 53. Output Voltage Waveforms
FS
R
, and the common-mode level of the output.
O
O
O
, is used to convert each of the comple-
O
. Figure 53 illustrates the output voltage
PEAK
IOUT1P
IOUT1N
IOUT2P
IOUT2N
V
P
, is calculated as
R
R
R
R
O
O
O
O
CM
, is calculated as
V
V
V
V
V
IP
IN
QP
QN
V
V
OUT
OUTQ
OUTI
+
–
+
–
OUT
Rev. A | Page 40 of 56
.
AUXILIARY DAC OPERATION
The AD9146 has two auxiliary DACs: one associated with the
I path and one associated with the Q path. These auxiliary DACs
can be used to compensate for dc offsets in the transmitted signal.
Each auxiliary DAC has a single-ended current that can sink or
source current into either the positive (P) or negative (N) out-
put of the associated transmit DAC. The auxiliary DAC
structure is shown in Figure 55.
The control registers for the I and Q auxiliary DACs are
Register 0x42, Register 0x43, Register 0x46, and Register 0x47.
Figure 54. IMD vs. Output Common-Mode Voltage (f
–50
–55
–60
–65
–70
–75
–80
–85
R
0
LOAD
I
I
I
FS
FS
FS
= 50 Ω Differential, I
I AUX DAC[9:0]
= 10mA
= 20mA
= 30mA
0.2
DIRECTION
I AUX DAC
I AUX DAC
Figure 55. Auxiliary DAC Structure
CURRENT
I DAC
0.4
SIGN
0.6
V
FS
V
B
CM
= 10 mA, 20 mA, and 30 mA)
(V)
0.8
IOUT1P
IOUT1N
1.0
Data Sheet
OUT
1.2
= 161 MHz,
1.4