micrf112 Micrel Semiconductor, micrf112 Datasheet - Page 13

• Manufacturer Part Number: micrf112
• Description: Qwikradio Uhf Ask/fsk Transmitter
• Manufacturer: Micrel Semiconductor

Crystal Oscillator for FSK Operation
Figure 5 shows reference oscillator circuit configuration
for FSK operation. To operate the MICRF112 in FSK
mode, one additional capacitor is needed between
XTALOUT pin and XTALMOD pin. Crystal parameters
for FSK operation are the same as ASK operation
except:
PLL ×32
The function of PLL×32 is to provide a stable carrier
frequency for transmission. It is a “divided by 32” phase
locked oscillator.
Micrel, Inc.
March 2008
•
•
Figure 5. Reference Oscillator FSK Operation
When the ESR of crystal is at 20Ω, C
not to exceed 70pF.
When the ESR of crystal is at 300Ω, C
C
LOAD
not to exceed 30pF
FSK
+ C
FSK
LOAD
+
13
Power Amplifier
The power amplifier serves two purposes: 1) to buffer
the VCO from external elements and 2) to amplify the
phase locked signal. The power amplifier can produce
+10dBm at 3V (typical).
Enable Control
Enable control gates the ASK data. It only allows
transmission when Lock, Amplitude and Under Voltage
Detect conditions are valid.
Under Voltage Detect
“Under voltage detect” block senses operating voltage.
If the operating voltage falls below 1.6V, “under voltage
detect” block will send a signal to “enable control” block
to disable the PA.
Open Drain Switch
Open drain switch is used for FSK operation. FSK data
is fed into the FSK pin. The FSK pin is connected to the
gate of the open drain switch. The open collector is
connected to the XTALMOD pin. In Figure 4, a capacitor
is shown connected from XTALMOD pin to XTALOUT.
When FSK pin goes high, the capacitor between
XTALMOD and XTALOUT pulls the frequency of
REFOSC low
[phone]
M9999-031008
MICRF112
.