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).
Fig. 6 Example of double conversion from VHF/UHF frequencies to TV IF
Optional application utilising
on–board crystal controlled
Fig. 7 Typical application, SP5658F
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.