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M491B Datasheet(PDF) 6 Page - STMicroelectronics

Part No. M491B
Description  SINGLE-CHIP VOLTAGE SYNTHESIS TUNING SYSTEM WITH 1 ANALOG CONTROL
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Maker  STMICROELECTRONICS [STMicroelectronics]
Homepage  http://www.st.com
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M491B Datasheet(HTML) 6 Page - STMicroelectronics

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PIN 3 : MEMORY TIMING OUTPUT
This output gives the timing for the pulses to be
applied at Pin 2 during the modify and read cycles.
The output consists of an open drain transistor.
PIN 4 : FINE TUNING D/A (see Figure 5)
A D/A converter with 16-step resolution and a fre-
quency of 15kHz can be used to generate a voltage
which, if fed to a varicap diode in parallel to the AFC
discriminator, will detune the receiver by a small
∆f
while maintaining the action of the Digital AFT. This
output can be used in conjunction with both Linear
and Digital AFT modes of operations.
The Fine tuning function operates as follows :
- At the start of any automatic or manual search,
the output is set at the mid range.
- When the search has been completed it is possi-
ble to operate on FT
± commands.
The store command memorizes this information
together with the 13 tuning voltage bits and 2
information bits.
- Modification time of FT D/A is of 1 step every
200ms if issued locally or every 2 received signals
from Remote control transmitter.
PIN 5 : TUNING D/A (see Figure 6)
A 2
13 = 8192 step pulse modulated signal for the
tuning voltage is available on this pin.
Pulse modulation is implemented by combination
of a rate multiplier and pulse width principle.
With a tuning voltage increasing from zero, the
number of pulses increases continuously up to
2
8 = 256 ; starting from this point the number of
pulses remains the same but the pulses get larger
until they reach the maximum content of the inter-
nal counter. The output consists of an open drain
transistor which offers a low impedance to ground
when in the ON state.
V
OUT
9
7
FT
FT
64
µs
Mid
Range
Fine Tuning Output
Figure 5
M491B
6/16


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