ADF4351BCPZ AD [Analog Devices], ADF4351BCPZ Datasheet - Page 13

• Manufacturer Part Number: ADF4351BCPZ
• Description: Wideband Synthesizer
• Manufacturer: AD [Analog Devices]

Data Sheet
The R counter output is used as the clock for the band select
logic. A programmable divider is provided at the R counter
output to allow division by an integer from 1 to 255; the divider
value is set using Bits[DB19:DB12] in Register 4 (R4). When the
required PFD frequency is higher than 125 kHz, the divide ratio
should be set to allow enough time for correct band selection.
Band selection takes 10 cycles of the PFD frequency, equal to
80 µs. If faster lock times are required, Bit DB23 in Register 3
(R3) must be set to 1. This setting allows the user to select a
higher band select clock frequency of up to 500 kHz, which
speeds up the minimum band select time to 20 µs. For phase
adjustments and small (<1 MHz) frequency adjustments, the
user can disable VCO band selection by setting Bit DB28 in
Register 1 (R1) to 1. This setting selects the phase adjust feature.
After band selection, normal PLL action resumes. The nominal
value of K
VCO output or from this value divided by D. D is the output
divider value if the N divider is driven from the RF divider output
(selected by programming Bits[DB22:DB20] in Register 4). The
ADF4351
ation of the product of I
constant.
The VCO shows variation of K
band and from band to band. For wideband applications cover-
ing a wide frequency range (and changing output dividers), a
value of 40 MHz/V provides the most accurate K
value is closest to an average value. Figure 21 shows how K
varies with fundamental VCO frequency, along with an average
value for the frequency band. Users may prefer this figure when
using narrow-band designs.
80
70
60
50
40
30
20
10
0
2.0
V
contains linearization circuitry to minimize any vari-
is 40 MHz/V when the N divider is driven from the
Figure 21. VCO Sensitivity (K
2.5
CP
and K
FREQUENCY (GHz)
3.0
V
V
as the V
to keep the loop bandwidth
3.5
V
) vs. Frequency
TUNE
varies within the
4.0
V
because this
4.5
V
Rev. 0 | Page 13 of 28
OUTPUT STAGE
The RF
to the collectors of an NPN differential pair driven by buffered
outputs of the VCO, as shown in Figure 22.
To allow the user to optimize the power dissipation vs. the
output power requirements, the tail current of the differential
pair is programmable using Bits[DB4:DB3] in Register 4 (R4).
Four current levels can be set. These levels give output power
levels of −4 dBm, −1 dBm, +2 dBm, and +5 dBm, using a 50 Ω
resistor to AV
both outputs can be combined in a 1 + 1:1 transformer or a 180°
microstrip coupler (see the Output Matching section).
If the outputs are used individually, the optimum output stage
consists of a shunt inductor to V
output must be terminated with a similar circuit to the used output.
An auxiliary output stage exists on the RF
pins, providing a second set of differential outputs that can be
used to drive another circuit. The auxiliary output stage can be
used only if the primary outputs are enabled. If the auxiliary
output stage is not used, it can be powered down.
Another feature of the
the RF output stage can be shut down until the part achieves
lock, as measured by the digital lock detect circuitry. This
feature is enabled by setting the mute till lock detect (MTLD)
bit in Register 4 (R4).
OUT
VCO
A+ and RF
DD
and ac coupling into a 50 Ω load. Alternatively,
DIVIDE-BY-1/-2/-4/-8/
-16/-32/-64
BUFFER/
OUT
Figure 22. Output Stage
ADF4351
A− pins of the
VCO
is that the supply current to
. The unused complementary
RF
OUT
ADF4351
A+
OUT
B+ and RF
RF
OUT
are connected
ADF4351
A–
OUT
B−