SL1461 Mitel Networks Corporation, SL1461 Datasheet - Page 10

• Manufacturer Part Number: SL1461
• Description: Wideband PLL FM Demodulator
• Manufacturer: Mitel Networks Corporation

10
SL1461SA
Lock range
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
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
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.
Lock range should be symmetric about the centre of the
The standard application circuit for the SL1461SA is
The VCO should be set up so that the desired input 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 V
the FM deviation of the squarewave used, the more accurate
the setting will be.
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.
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.
The easiest way to centralise the VCO is to input an RF
A pre-emphasised video input containing black to white
The setting can be confirmed by measuring the DC
CC-0.7V
. The smaller