micrf213 Micrel Semiconductor, micrf213 Datasheet - Page 10

• Manufacturer Part Number: micrf213
• Description: Micrf213 3.3v, Qwikradio 315mhz Receiver
• Manufacturer: Micrel Semiconductor

the top layer close to the REFOSC pins RO1 and
RO2. When care is not taken in the layout, and
crystals from other vendors are used, the oscillator
may take longer times to start as well as the time to
good data in the DO pin to show up. In some cases, if
the stray capacitance is too high (>20pF), the
oscillator may not start at all.
The crystal frequency is calculated by REFOSC = RF
Carrier/(32+(1.1/12)). The local oscillator is low side
injection (32 × 9.81563MHz = 314.1MHz), that is, its
frequency is below the RF carrier frequency and the
image frequency is below the LO frequency. Refer to
Figure 6. The product of the incoming RF signal and
local oscillator signal will yield the IF frequency, which
will then be demodulated by the detector of the
device.
JP1 and JP2 are the bandwidth selection for the
demodulator bandwidth. To set it correctly, it is
necessary to know the shortest pulse width of the
encoded data sent in the transmitter. Reference the
example of the data profile, in the Figure 7, below:
PW2 is shorter than PW1, so PW2 should be used for
the
calculation is found by 0.65/shortest pulse width. After
this value is found, the setting should be done
REFOSC
(MHz)
9.467411
9.81563
10.75045
Micrel, Inc.
May 2007
Table 5. Crystal Frequency and Vendor Part Number
Frequency
Figure 6. Low Side Injection Local Oscillator
demodulator
Image
Figure 7. Example of a Data Profile
Carrier
(MHz)
303.825
315
345.0
bandwidth
HIB Part Number
SA-9.467411-F-10-H-30-30-X
SA-9.815630-F-10-H-30-30-X
SA-10.750450-F-10-H-30-30-X
f
LO
calculation.
Desired
f (MHz)
Signal
The
10
according to Table 6. For example, if the pulse period
is 140µsec, 50% duty cycle, then the pulse width will
be 70µsec (PW = (140 µsec * 50%) / 100). So, a
bandwidth of 9.286kHz would be necessary (0.65 /
70µsec). However, if this data stream had a pulse
period with a 20% duty cycle, then the bandwidth
required would be 23.2kHz (0.65 / 28µsec), which
exceeds the maximum bandwidth of the demodulator
circuit. If one tries to exceed the maximum bandwidth,
the pulse would appear stretched or wider.
Capacitors C6 and C4, Cth and Cagc capacitors
respectively, provide the time base reference for the
data pattern received. These capacitors are selected
according to data profile, pulse duty cycle, dead time
between two received data packets and if the data
pattern has or not a preamble. See Figure 7 for an
example of a data profile.
Other frequencies will have different demodulator
bandwidth limits, which are derived from the reference
oscillator frequency. Table 7 and Table 8, below,
show the limits for the other two most used
frequencies.
SEL0
SEL0
SEL0
Short
Open
Short
Open
Short
Open
Short
Open
Short
Open
Short
Open
JP1
JP1
JP1
Table 7. JP1 and JP2 Setting, 303.825MHz
Table 8. JP1 and JP2 Setting, 345.0MHz
Table 6. JP1 and JP2 Setting, 315MHz
SEL1
Open
Open
SEL1
Open
Open
SEL1
Open
Open
Short
Short
Short
Short
Short
Short
JP2
JP2
JP2
Demod.
Demod.
Demod.
(hertz)
(hertz)
(hertz)
10340
1180
2360
4720
9400
1140
2280
4550
9100
1290
2580
5170
BW
BW
BW
Shortest
Shortest
Shortest
(usec)
(usec)
(usec)
Pulse
Pulse
Pulse
551
275
138
570
285
143
504
252
126
69
71
63
M9999-052307-A
[phone]
baud rate for
baud rate for
baud rate for
Cycle (Hertz)
Cycle (hertz)
Cycle (hertz)
MICRF213
Maximum
Maximum
Maximum
50% Duty
50% Duty
50% Duty
1815
3631
7230
8770
1754
3500
7000
1985
3977
7954
908
992