Micrel MICRF506, Руководство пользователя

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Micrel MICRF506
Transmitter
Power Amplifier
A6..A0 D7 D6 D5 D4 D3 D2 D1 D0
0000000 LNA_by PA2 PA1 PA0 Sync_en Mode1 Mode0 Load_en
0000001 Modulation1 Modulation0 ‘0’ ‘0’ RSSI_en LD_en PF_FC1 PF_FC0
0000010 CP_HI SC_by ‘0’ PA_By OUTS3 OUTS2 OUTS1 OUTS0
The maximum output power is approximately 10dBm
for a 50
Ω load. For maximum output power the load
seen by the PA must be resistive. Higher output
power can be obtained by decreasing the load
impedance. However, this will be in conflict with
obtaining impedance match in the LNA. The output
power is programmable in seven steps, with
approximately 3dB between each step. This is
controlled by bits PA2 – PA0.
July 2006 24 M9999-092904
+1 408-944-0800
The power amplifier can be turned off by setting PA2
– PA0 = 0.
For all other combinations the PA is on and has
maximum power when PA2 – PA0 = 1.
The PA will be bypassed if PA_by=1. Output power
will drop ~22dB. It is still possible to control the
power by PA2 – PA0.
The output power varies about 3dB over power
supply 2.0V to 2.5V and about 2dB over temperature
-40
˚ C to +85 ˚ C. The 2
nd
and 3
rd
harmonic of the PA
are as follows:
2
nd
harmonic: <-16dBm
3
rd
harmonic: <-8dBm
To reduce the emission of harmonics, an LC filter
can be added between the ANT pin and the antenna
as shown in Figure 15.
C4
18pF
C5
47pF
15pF
C6
L1
12nH
ANT
Figure 15. LC Filter
This filter is designed for the 434MHz band with
50Ohm terminations. The component values may
have to be tuned to compensate for the layout
parasitics. This filter may also increase the receiver
selectivity.
Frequency Modulation
A6..A0 D7 D6 D5 D4 D3 D2 D1 D0
0000001 Modulation1 Modulation0 ‘0’ ‘0’ RSSI_en LD_en PF_FC1 PF_FC0
Modulation1 Modulation0 Modulation Type
0 0 Closed loop modulation
using modulator
0 1 Not in use
1 0 FSK applied using two
sets of dividers
1 1 Not in use
Table 11. Modulation Bit Setting
When Modulation1 and Modulation0 is 00, the
modulator needs to be programmed properly, see
“Modulator” section. The modulation signal will now
be applied directly on the phase locked VCO. It is
therefore important that the PLL bandwidth is not too
high, as this will remove the modulation. See “PLL
Filter” section on how to calculate the PLL
components. When using the modulator the
modulation signal is applied to the VCO and
therefore some sort of encoding is needed.
The level of encoding is determined by the PLL loop
filter bandwidth and data rate. Two of the most
common encoding techniques are Manchester
encoding and 3B4B. Other encoding schemes may
also be used.
Manchester encoding is when one bit is encoded in
to a two-bit word and is shown in Table 10. When
using Manchester encoding the maximum overhead
is 100%. When selecting PLL loop filter it is
important to note that the min baud rate is equal to:
f
baud_min
=
baud /s
4
f
baud_min
: The minimum frequency of the baud
rate [Hz]
baud/s: Elements per second (encoded data)
Data Word
“0” “10”
“1” “01”