8

SP5658

DOUBLE CONVERSION TUNER SYSTEMS

The high 2.7GHz maximum operating frequency and

excellent noise characteristics of the SP5658 enables the

construction of double conversion high IF tuners.

A typical system shown in Fig.7 will use the SP5658 as the

first LO control for full band upconversion to an IF of greater

than 1GHz. The wide range of reference division ratios allows

the SP5658 to be used both for the up converter LO with a high

phase comparator frequency (hence low phase noise) and the

down converter which utilises the device in a lower

comparison frequency mode (which offers a fine step size).

50–900MHz

1.6GHz

38.9MHz

1650–2700MHz

SP5658

SP5658

First LO

Second LO

CONTROL

MICRO

15nF

68pF

+30V

+5V

22k

16k

47k

+12V

2n2

2N3904

1n

1n

10n

P1

TUNER

OSCILLATOR

OUTPUT

13k3

P0

DIS

LOCK

CLOCK

DATA

ENABLE

REF 10n

18pF

4MHz

Optional application utilising

on–board crystal controlled

oscillator

114

2

3

4

5

6

7

13

12

11

10

8

9

APPLICATION NOTES

A generic set of application notes AN168 for designing

with synthesisers such as the SP5658 has been written. This

covers aspects such as loop filter design and decoupling. This

application note is also featured in the Media IC Handbook.

A generic test/demo board has been produced which can

be used for the SP5658. A circuit diagram and layout for the

board is shown in Figs. 8 and 9.

The board can be used for the following purposes:

(A) measuring RF sensitivity performance.

(B) Indicating port function.

(C) Synthesising a voltage controlled oscillator.

(D) Testing of external reference sources.

Fig. 6 Example of double conversion from VHF/UHF frequencies to TV IF

Fig. 7 Typical application, SP5658F