micrf506 Micrel Semiconductor, micrf506 Datasheet - Page 13

• Manufacturer Part Number: micrf506
• Description: 410mhz And 450mhz Ism Band Transceiver
• Manufacturer: Micrel Semiconductor

0001001
Frequency Synthesizer
The frequency synthesizer consists of a voltage-
controlled oscillator (VCO), a crystal oscillator, dual
modulus prescaler, programmable frequency
dividers and a phase-detector. The loop-filter is
external for flexibility and can be a simple passive
circuit. The lengths of the N, M, and A registers
are12, 12 and 6 respectively. The M, N, and A
values can be calculated from the formula:
where fPhD is the phase detector comparison
frequency.
PhD: Phase detector comparison frequency
fxco: Crystal oscillator frequency
fvco: Voltage controlled oscillator frequency
There are two sets of each of the divide factors (i.e.
A0 and A1). If modulation by using the dividers is
selected (that is Modulation1=1, Modulation0=0), the
two sets should be programmed to give two RF
frequencies, separated by two times the specified
frequency deviation. For all other modulation
methods, and also in receive mode, the 0-set will be
used.
Crystal Oscillator (XCO)
The crystal oscillator is a very critical block. As the
crystal oscillator is a reference for the RF output
frequency and also for the LO frequency in the
receiver, very good phase and frequency stability is
The crystal used is a TN4-26011 from Toyocom.
Adr
Micrel
September 2004
0001010
0001011
0001100
0001101
0001110
0001111
0010000
0010001
0010010
0010011
A6…A0
D7
‘0’
fPDH =
D6
‘1’
D5
‘1’
M0_7
M1_7
XCOtune4 XCOtune3 XCOtune2
N0_7
N1_7
f
D7
XCO
M
-
-
-
-
-
-
D4
=
31
N + A
f
D3
VCO
M0_6
M1_6
N0_6
N1_6
D6
-
-
-
-
-
-
=
D2
31
N + A
f
RF

4
XCOtune1
M0_5
M1_5
A0_5
N0_5
A1_5
N1_5
D1
D5
-
-
-
-
XCOtune0
D0
M0_4
M1_4
A0_4
N0_4
A1_4
N1_4
13
D4
-
-
-
-
required. The schematic of the crystal oscillator’s
external components for 16MHz are shown in Figure
5.
The crystal should be connected between pins
XosIn and XoscOut (pin 23 and 23). In addition,
loading capacitors for the crystal are required. The
loading capacitor values depend on the total load
capacitance, C
capacitance seen between the crystal terminals
should be equal to C
the specified frequency.
The parasitic capacitance is the pin input
capacitance and PCB stray capacitance. Typically,
the total parasitic capacitance is around 6pF. For
instance, for a 9pF load crystal the recommended
values of the external load capacitors are 5.6pF.
It is also possible to tune the crystal oscillator
internally by switching in internal capacitance using
5 tune bits XCOtune4 – XCOtun0. When XCOtune4
– XCOtune0 = 0 no internal capacitors are
connected to the crystal pins. When XCOtune4 –
XCOtune0 = 1 all of the internal capacitors are
connected to the crystal pins. Figure 3 shows the
tuning range for two different capacitor values, there
are 1.5pF and no capacitors.
Specification: Package TSX-10A, Nominal frequency
M0_11
M1_11
N0_11
N1_11
M0_3
M1_3
N0_3
N1_3
XTALOUT
A0_3
A1_3
D3
Pin 24
Figure 5. Crystal Oscillator Circuit
C
L
L
, specified for the crystal. The load
M0_10
M1_10
N0_10
N1_10
=
M0_2
M1_2
N0_2
N1_2
A0_2
A1_2
D2
C10
5.6pF
C
L
1
10
for the crystal to oscillate at
1
+
C
1
11
Y1
TSX-10A
+ C
M0_9
M0_1
M1_9
M1_1
A0_1
N0_9
N0_1
A1_1
N1_9
N1_1
D1
parasitic
C11
5.6pF
[phone]
M9999-092904
MICRF506
XTALIN
Pin 23
M0_0
M1_0
M0_8
M1_8
A0_0
N0_8
N0_0
A1_0
N1_8
N1_0
D0