MICRF600_06 Datasheet, PDF (12/21 Pages) Micrel Semiconductor – 902-928MHz ISM Band Transceiver Module

Micrel, Inc.
MICRF600/MICRF600Z
Frequency Synthesizer
A6…A0
0001010
0001011
0001100
0001101
0001110
0001111
0010000
0010001
0010010
s0010011
D7
-
-
N0_7
-
M0_7
-
-
N1_7
-
M1_7
D6
-
-
N0_6
-
M0_6
-
-
N1_6
-
M1_6
D5
A0_5
-
N0_5
-
M0_5
A1_5
-
N1_5
-
M1_5
D4
A0_4
-
N0_4
-
M0_4
A1_4
-
N1_4
-
M1_4
D3
A0_3
N0_11
N0_3
M0_11
M0_3
A1_3
N1_11
N1_3
M1_11
M1_3
D2
A0_2
N0_10
N0_2
M0_10
M0_2
A1_2
N1_10
N1_2
M1_10
M1_2
D1
A0_1
N0_9
N0_1
M0_9
M0_1
A1_1
N1_9
N1_1
M1_9
M1_1
D0
A0_0
N0_8
N0_0
M0_8
M0_0
A1_0
N1_8
N1_0
M1_8
M1_0
The frequency synthesizer consists of a voltage-controlled
oscillator (VCO), a crystal oscillator, phase select
prescaler, programmable frequency dividers and a phase-
detector. The length of the N, M, and A registers are 12,
12 and 6 respectively. The N, M, and A values can be
calculated from the formula:
f _PhD
=
f _XCO
M
=
f _VCO
(16 × N + A)× 2
=
(16
f _RF
×N
+
A
)
,
M≠0
1≤A<N
f_PHD: Phase detector comparison frequency
f_XCO: Crystal oscillator frequency
f_VCO: Voltage controlled oscillator frequency
f_RF: Input/output RF frequency
There are two sets of each of the divide factors (i.e. A0
and A1). Storing the ‘0’ and the ‘1’ frequency in the 0- and
the 1 registers respectively, does the 2-FSK. The receive
frequency must be stored in the ‘0’ registers.
Crystal Oscillator (XCO)
Adr
D7 D6 D5
D4
0001001 ‘0’ ‘0’ ‘1’ XCOtune4
D3
XCOtune3
D2
XCOtune2
D1
XCOtune1
D0
XCOtune0
The crystal oscillator is a reference for the RF output
frequency and the LO frequency in the receiver. It is
possible to tune the internal crystal oscillator by switching
in internal capacitance using 5 tune bits XCOtune4 –
XCOtun0. The benefit of tuning the crystal oscillator is to
eliminate the initial tolerance and the tolerance over
temperature and aging. By using the crystal tuning feature
the noise bandwidth of the receiver can be reduced and a
higher sensitivity is achieved. 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 5 shows the tuning range.
55.0
45.0
35.0
25.0
15.0
5.0
-5.0
-15.0
-25.0
-35.0
-45.0
0 4 8 12 16 20 24 28 32
[XCO_tune value]
Figure 5. XCO Tuning
The typical start up time for the crystal oscillator (default
XCO_tune=13) is ~750us. If more capacitance is added
(higher XCO_tune value), then the start-up time will be
longer.
To save current in the crystal oscillator start-up period, the
XCO is turned on before any other circuit block. When the
XCO has settled, rest of the circuit will be turned on. No
programming should be made during this period.
The current consumption during the prestart period is
approximately 280µA.
VCO
A6..A0 D7 D6 D5
D4
D3
D2
D1
D0
0000011 ‘1’ ‘1’ ‘0’ VCO_IB2 VCO_IB1 VCO_IB0 VCO_freq1 VCO_freq0
The VCO has no external components. It has three bit to
set the bias current and two bit to set the VCO frequency.
These five bits are set by the RF frequency, as follows:
RF freq.
915MHz
950MHz
VCO_IB2
0
0
VCO_IB1
0
0
VCO_IB0 VCO_freq1 VCO_freq0
1
1
0
0
1
1
Table 7. VCO Bit Setting
The bias bit will optimize the phase noise, and the
frequency bit will control a capacitor bank in the VCO. The
tuning range the RF frequency versus varactor voltage is
dependent on the VCO frequency setting, and can be
shown in Figure 6.
July 2006
12
M9999-082505