NJ88C33
VCO Driving Without Voltage Doubler
To switch off the voltage doubler, bit 7 of the status register
is programmed low. This will reduce current consumption and
minimise noise. The voltage doubler output C should be
connected to GND1 as connection to GND2 would induce
noise in the VCO loop.
VCO Driving With Voltage Doubler
The voltage doubler is switched on by setting bit 7 of the
status register high. It is recommended that a reservoir
capacitor of at least 1µF be connected from C to GND1.
The voltage doubler is designed to boost VCO drive in low
voltage applications.
Fig. 9 Driving a VCO without voltage doubler
Fig. 10 Driving a VCO using the voltage doubler
Further Applications Information
A stand-alone programmer card and an evaluation board
are available for evaluating the NJ88C33. The programmer
card allows two sets of variables to be programmed into both
the divider and status registers during alternate programming
cycles, at either the standard I
2
C bus rate of 100kHz or at
2MHz.
Initialisation is with either a manual push-button or by an
external logic level pulse; a synchronisation output is provided
to allow a quick assessment of ‘step’ and ‘settle’ responses to
be made.
The NJ88C33 evaluation board (Fig. 11 ) dernonstrates
the preferred layout technique - providing a reference
oscillator, a 60 to 80MHz VCO and a simple loop filter to
complete a minimal frequency synthesiser loop. The two units
allow analysis of different loop variables as well as the
selection of comparison frequencies for fast frequency-
hopping loops.
Application Note: AN94,
‘Using
the NJ88C33
PLL
Synthesiser’
explains the design equations and
demonstrates the use of the device, and is available from your
local Mitel Semiconductor customer service centre.
9
MITEL [ MITEL NETWORKS CORPORATION ]
