AD9122-M5372-EBZ Analog Devices Inc, AD9122-M5372-EBZ Datasheet - Page 46

• Manufacturer Part Number: AD9122-M5372-EBZ
• Description: DAC Evaluation Board W/ ADL5372 Modulator
• Manufacturer: Analog Devices Inc
• Series: TxDAC+®r

Specifications of AD9122-M5372-EBZ

• Silicon Manufacturer: Analog Devices
• Application Sub Type: DAC
• Kit Application Type: Data Converter
• Silicon Core Number: AD9122
• Number Of Adc's: 2
• Number Of Bits: 16
• Sampling Rate (per Second): 1.2G
• Data Interface: Serial
• Inputs Per Adc: 1 Differential
• Power (typ) @ Conditions: 800mW @ 500MSPS
• Operating Temperature: -40°C ~ 85°C
• Utilized Ic / Part: AD9122, ADL5372
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD9122
PLL Settings
There are three settings for the PLL circuitry that should be
programmed to their nominal values. The PLL values shown in
Table 24 are the recommended settings for these parameters.
Table 24. PLL Settings
PLL SPI Control
PLL Loop Bandwidth[1:0]
PLL Charge Pump Current[4:0]
PLL Cross Control Enable
Configuring the VCO Tuning Band
The PLL VCO has a valid operating range from approximately
1.0 GHz to 2.1 GHz covered in 63 overlapping frequency bands.
For any desired VCO output frequency, there may be several
valid PLL band select values. The frequency bands of a typical
device are shown in Figure 66. Device-to-device variations and
operating temperature affect the actual band frequency range.
Therefore, it is required that the optimal PLL band select value
be determined for each individual device.
Automatic VCO Band Select
The device has an automatic VCO band select feature on chip.
Using the automatic VCO band select feature is a simple and
reliable method of configuring the VCO frequency band. This
feature is enabled by starting the PLL in manual mode, then
placing the PLL in auto band select mode. This is done by
setting Register 0x0A to a value of 0xCF, then to a value of
0xA0. When these values are written, the device executes an
automated routine that determines the optimal VCO band
setting for the device. The setting selected by the device ensures
that the PLL remains locked over the full −40°C to +85°C
operating temperature range of the device without further
adjustment. (The PLL remains locked over the full temperature
range even if the temperature during initialization is at one of
the temperature extremes.)
Figure 66. PLL Lock Range Over Temperature for a Typical Device
12
16
20
24
28
32
36
40
44
48
52
56
60
1000
0
4
8
1200
1400
VCO FREQUENCY (MHz)
1600
0x0C
Address
Register
0x0C
0x0D
1800
Bit
[7:6]
[4:0]
[4]
2000
Optimal
Setting
11
10001
1
2200
Rev. A | Page 46 of 60
Manual VCO Band Select
The device also has a manual band select mode (PLL manual
enable, Register 0x0A, Bit[6] = 1) that allows the user to select
the VCO tuning band. When in manual mode, the VCO band
is set directly with the value written to the manual VCO band,
(Register 0x0A, Bit[5:0]). To properly select the VCO band,
follow these steps:
1.
2.
3.
4.
5.
Table 25. VCO Control Voltage Range Indications
VCO Control Voltage
1111
1110
1101
1100
1011
1010
1001
1000
0111
0110
0101
0100
0011
0010
0001
0000
Put the device in manual band select mode.
Sweep the VCO band over a range of bands that result in
the PLL being locked.
For each band, verify that the PLL is locked and read the
PLL using the VCO control voltage (Register 0x0E[3:0]).
Select the band that results in the control voltage being
closest to the center of the range (that is, 0000 or 1000). See
Table 25 for more details. The resulting VCO band should
be the optimal setting for the device. Write this band to the
manual VCO band (Register 0x0A[5:0]) value.
If desired, an indication of where the VCO is within the
operating frequency band can be determined by querying
the VCO control voltage. Table 25 shows how to interpret
the PLL VCO control voltage (Register 0x0E, Bits[2:0]) value.
Indication
Move to higher VCO band
VCO is operating in the higher end of
frequency band
VCO is operating within an optimal
region of the frequency band
VCO is operating in the lower end of
frequency band
Move to lower VCO band