Datasheet

Data Sheet ADF4007
Rev. B | Page 11 of 16
APPLICATIONS INFORMATION
FIXED HIGH FREQUENCY LOCAL OSCILLATOR
Figure 13 shows the ADF4007 being used with the HMC358MS8G
VCO from Hittite Microwave Corporation to produce a fixed-
frequency LO (local oscillator), which could be used in satellite
or CATV applications. In this case, the desired LO is 6.7 GHz.
The reference input signal is applied to the circuit at FREF
IN
and, in this case, is terminated in 50 Ω. Many systems would
have either a TCXO or an OCXO driving the reference input
without any 50 Ω termination. To bias the REF
IN
pi n at AV
DD
/2,
ac coupling is used. The value of the coupling capacitor used
depends on the input frequency. The equivalent impedance at
the input frequency should be less than 10 Ω. Given that the dc
input impedance at the REF
IN
pin is 100 kΩ, less than 0.1% of
the signal is lost.
The charge pump output of the ADF4007 drives the loop filter.
In calculating the loop filter component values, a number of items
need to be considered. In this example, the loop filter was designed
so that the overall phase margin for the system is 45°.
Other PLL system specifications are as follows:
K
D
= 5 mA
K
V
= 100 MHz/V
Loop Bandwidth = 300 kHz
F
PFD
= 106 MHz
N = 64
All these specifications are needed and used with the ADIsimPLL
to derive the loop filter component values shown in Figure 13.
The circuit in Figure 13 gives a typical phase noise performance
of −100 dBc/Hz at 10 kHz offset from the carrier. Spurs are
heavily attenuated by the loop filter and are below −90 dBc.
The loop filter output drives the VCO, which, in turn, is fed
back to the RF input of the PLL synthesizer and also drives the
RF output terminal. A T-circuit configuration provides 50 Ω
matching between the VCO output, the RF output, and the RF
IN
terminal of the synthesizer.
ADF4007
N2
N1
M2
M1
100pF 100pF
100pF
CP
MUXOUT
GND GND GND
5.6nF
51Ω
18Ω
22Ω
NOTE
DECOUPLING CAPACITORS (0.1mF/10pF) ON AV
DD
, DV
DD
, AND V
P
OF THEADF4007 AND ON
V
CC
OF THEAD820 AND THE HMC358MS8G HAVE BEEN OMITTED FROM THE DIAGRAM
TO AID CLARITY.
R
SET
AV
DD
DV
DD
V
P
FREF
IN
VCO
100MHz/V
HMC358MS8G
R
SET
5.1kΩ
6
17
18
8
20
15
19
9
3
2
10
04537-019
RF
IN
A
RF
IN
B
5
4
11
12
13
14
GND
47nF
AV
DD
7
DV
DD
16
REF
IN
AV
DD
= 3.3V
1kΩ
18kΩ
V
CC
= 12V
V
CC
= 3.3V
1kΩ
AD820
10pF
18Ω
100pF
18Ω
100pF
RF
OUT
LOGIC HI
LOGIC HI
LOGIC LO
LOGIC LO
Figure 13. 6.78 GHz Local Oscillator Using the ADF4007