
Fig. 12
Pins 5 and 6 (VIF input)
These are the VIF amplifier input pins. The inputs must always
have their DC components eliminated with capacitors. The
inputs are equilibrium inputs.
The input impedance is R
6
1.5 k
, C
6
3 pF.
Sanyo’s SAW filter
There are two types of filters, depending on the piezoelectric substrate material.
(1) LiTaO
3
(lithium tantalate) SAW filters: ...... TSF1xxx
TSF2xxx
While the LiTaO
3
SAW filters offer excellent stability with a low temperature coefficient of –18 ppm/ °C, the insertion loss
is high. However, by using a coil, etc., for matching on the SAW filter output side (which does increase the number of
external components), it is possible to suppress the insertion loss while at the same time making the level of the
characteristics variable, which provides additional design freedom. (Refer to Fig. 13.)
In addition, because the SAW (surface wave) reflection is small, ripple within the band can be kept low.
(2) LiNbO
3
(lithium niobate) SAW filter: ...... TSF5xxx
While the LiNbO
3
SAW filter has a high temperature coefficient of 72 ppm/ °C, it has a lower insertion loss by about
10 dB compared to the LiTaO
3
SAW filters. Therefore, matching on the output side of the SAW filter is not necessary. (Refer
to Fig. 14.)
In addition, because the insertion loss is low (although the ripple within the band is somewhat higher than in the case of the
LiTaO
3
SAW filter), the low impedance and small feedthrough diminish the effects of peripheral circuit components and the
pattern layout, and make it possible to stabilize the trap characteristics outside of the band.
From the above, it is clear that the LiTaO
3
SAW filter is suitable for Japan and U.S. bands where the IF frequency is high, while
the LiNbO
3
SAW filter is suitable for PAL and U.S. bands where the IF frequency is low.
0.01μF
Fig. 13
Fig. 14
0.01μF
LA7578N
No.4037-11/18