MC13001XP Просмотр технического описания (PDF) - Motorola => Freescale
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MC13001XP Datasheet PDF : 10 Pages
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MC13001X MC13007X
The oscillator itself is a novel design using an on–chip
50 pF silicon nitride capacitor which has a temperature drift
of only 70 ppm/°C and negligible long term drift. This, in
conjunction with an external resistor, gives a drift of horizontal
frequency of less than 1.0 Hz/°C – i.e., less than 100 Hz over
the full operating temperature range of the chip. The pull–in
range of the PLL is about ±750 Hz, so normally this would
eliminate the need for any customer adjustment of the
frequency.
The second significant feature of this design is the use of a
virtual ground at the frequency control point which floats at a
potential derived from a divider across the power supply and
this is the same divider which determines the end–points of
the oscillator ramp. The frequency adjustment which is
necessary to take up tolerances in the on–chip capacitor is
fed in as a current to this virtual ground, and when this
adjustment current is derived from an external potentiometer
across the same supply there is no frequency variation with
supply voltage. Moreover, using the voltage from a
potentiometer for the adjustment instead of the simple
variable resistor normally used in RC oscillators makes the
frequency independent of the value of the potentiometer and
hence its temperature coefficient. The frequency control
current from the first phase detector is fed into this same
virtual ground, and as the sensitivity of the control is about
230 Hz/µA, a high value resistor can be used (680 kΩ) which
can be directly connected to the phase detector filter without
significant loading.
This oscillator operates with almost constant frequency
to below 4.0 V and as the total PLL system consumes
less than 4.0 mA at this voltage, this gives an ideal
startup characteristic for receivers using deflection–derived
power supplies.
The flyback gating input is on Pin 15 which is internally
clamped to 0.7 V in both directions and requires a negative
input current of 0.6 mA to operate the gate circuit. This input
can be a raw flyback pulse simply fed via a suitable resistor.
Vertical System
An output switching signal is taken from the 31.5 kHz
oscillator to clock the vertical counter which is used in place
of a conventional vertical oscillator circuit. The counter is
reset by the vertical sync pulse, but the period during which it
is permitted to reset is controlled by the window control.
Normally, when the counter is running synchronously, the
window is narrow to give some protection against spurious
noise pulses in the sync signal. If the counter output is not
coincident with sync however, after a short period the window
opens to five reset over a much wider count range, leading to
a fast picture roll towards lock. At weak signal, i.e., less than
200 µV IF input, the vertical system is forced to narrow mode
to give a steadier picture for commonly occurring types of
noise. The vertical sync, gated by the counter, then resets a
ramp generator on Pin 20 and the 1.5 Vpp ramp is
buffered to Pin 22 by the vertical preamplifier. A differential
input to the preamp on Pin 21 compares the signal generated
across the resistor in series with the deflection coils with the
generated ramp and thus controls shape and amplitude of
the coil current.
The basic block diagram of the countdown system is
shown in Figure 9. The 31.5 kHz (2FH) clock from the
horizontal oscillator drives a 10–stage counter circuit which is
normally reset by the vertical sync pulse via the sync gate,
‘‘OR’’ gate and D flip–flop. This D input is also used to initiate
discharge of the ramp capacitor and hence causes picture
flyback.
Figure 9. Monomax Vertical Countdown
0
Blanking
20
Latch
Blanking
Pulse
2FH
Clock
H/4
Delay
Coincidence
Detector
Vertical
Sync
10 Stage Counter
384–544
‘‘Wide’’
514–526
‘‘Narrow’’
Counter Reset
COINC
8H/2 Delay
To
‘‘Wide’’
Window
Control
COINC
2H/2 Delay
To
‘‘Narrow’’
Define
Window
for Sync
D
Sync Gate/
Ramp Latch
To Ramp
Pull–Down
D Flip–Flop
(Delay)
Clock
6
MOTOROLA ANALOG IC DEVICE DATA
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