ADF4007

Rev. 0 | Page 11 of 16

APPLICATIONS

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.

and, in this case, is terminated in 50 Ω. Many systems would

have either a TCXO or an OCXO driving the reference input

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

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:

Loop Bandwidth = 300 kHz

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

terminal of the synthesizer.

ADF4007

N2

N1

M2

M1

100pF

100pF

100pF

CP

MUXOUT

5.6nF

51

Ω

18

Ω

22

Ω

NOTE

TO AID CLARITY.

VCO

100MHz/V

HMC358MS8G

5.1k

Ω

6

17

18

8

20

15

19

9

3

2

10

5

4

11

12

13

14

GND

47nF

7

16

1k

Ω

18k

Ω

1k

Ω

AD820

10pF

18

Ω

100pF

18

Ω 100pF

LOGIC HI

LOGIC HI

LOGIC LO

LOGIC LO

Figure 13. 6.78 GHz Local Oscillator Using the ADF4007