SL1461MPAS datasheet(10/12 Pages) MITEL

10 / 12 page

SL1461SA

Lock range

Lock range should be symmetric about the centre of the

S-curve. When the oscillator is sitting in the centre of the

S-curve, the two video outputs will be at the same DC voltage.

RF oscillator design

The standard application circuit for the SL1461SA is

shown in Fig.3 The layout of the VCO tank should follow normal

good RF techniques - ie as compact as possible. This will

minimise parasitics, thus giving improved VCO linearity and

stability. The PCB layout used for testing purpose is shown in

Fig. 10.

Setting up of oscillator

The VCO should be set up so that the desired input RF

frequency is at the centre of the lock range. This will coincide

with the centre of the S-curve and the point at which the AFC

toggles when set to zero deadband.

The easiest way to centralise the VCO is to input an RF

carrier which is being modulated by a low frequency

squarewave. The tuning coil(s) should be adjusted until the

AFC voltage toggles between 0.2V and VCC-0.7V. The smaller

the FM deviation of the squarewave used, the more accurate

the setting will be.

A pre-emphasised video input containing black to white

transitions can also be used for this setting, since the DC

content in a pre-emphased video is much less than that in non

pre–emphasised video. This is important as any dc content in

the input waveform will introduce an offset in the AFC transition

point.

The setting can be confirmed by measuring the DC

voltage on the two video outputs, the voltages should be the

same when the oscillator is centred around the incoming

frequency. This DC measurement must be carried out with an

unmodulated carrier of the required frequency. Modulation

must not be present, since by definition, the dc voltages would

be changing, thus making accurate measurement difficult.

SL1461MPAS Arkusz danych(PDF) 10 Page - Mitel Networks Corporation