Datasheet
MC33411A/B
33
MOTOROLA RF/IF DEVICE DATA
Similarly, it can be shown:
A
openloop
+
–
K
pd
K
o
K
n
w
2
ǒ
(
C1
)
C2
)
C3
)
–
w
2
C1C2C3R2R3
Ǔ
)
1
)
j
w
T2
1
)
j
w
T1
(19)
In which:
T1
+
(
C1
)
C2
)
T2
)
(
C1C2
)
T3
C1
)
C2
)
C3
*
w
2
C1T2T3
(20)
T2
+
R2C2 T3
+
R3C3
(22)(21)
From T1 it can be derived that:
C2
+
(
T1
)
T2
)
C3
*
C1
ǒ
T2
)
T3
*
T1
)
w
2
T1T2T3
Ǔ
T3
*
T1
(23)
In analogy with (13), by forcing the loopgain to 1 (0 dB) at
ω
p
, we obtain:
C1
(
T1
)
T2
)
)
C2T3
)
C3T2
+
ǒ
K
pd
K
o
K
n
w
p
2
Ǔ
1
)
ǒ
w
p
T2
Ǔ
2
1
)
ǒ
w
p
T1
Ǔ
2
Ǹ
(24)
Solving for C1:
C1
+
(
T2
*
T1
)
T3C3
*
(
T3
*
T1
)
T2C3
)
(
T3
*
T1
)
ǒ
K
pd
K
o
T1
w
p
2
K
n
Ǔ
1
)
ǒ
w
p
T2
Ǔ
2
1
)
ǒ
w
p
T1
Ǔ
2
Ǹ
(
T3
*
T1
)
T2
)
(
T3
*
T1
)
T3
*
ǒ
T2
)
T3
*
T1
)
w
p
2
T1T2T3
Ǔ
T3
(25)
By selecting ω
p
via (12), the additional time constant
expressed as T3, can be set to:
T3
+
1
K
w
p
(26)
The K–factor shown determines how far the additional
pole frequency will be separated from ω
p
. Selecting too small
of a K–factor, the equations may provide negative
capacitance or resistor values. Too large of a K–factor may
not provide the maximum attenuation.
By selecting R3 to be 100 kΩ, C3 becomes known and C1
and C2 can be solved from the equations. By using equations
(11) and (10), time constants T2 and T1 can be derived by
selecting a phase margin. Finally, R2 follows from T2 and C2.
A test circuit with the following components and conditions
was constructed with these results:
Loop Filter (See Figure 49):
C1 = 470 pF
R2 = 68 kΩ
C2 = 3.9 nF
R3 = 270 kΩ
C3 = 82 pF
LO2 Tank:
Ctotal = 39.3 pF
Lext = 150 nH, Q = 50 @ 250 MHz
Reference Frequency = 10.24 MHz (unadjusted)
R Counter = 205
LO2 Counter = 1266
AC Load = 25 Ω
Frequency of LO2 = 63.258 MHz
Phase Noise @ 50 kHz offset = –107 dBc
Sidebands @ 50 kHz & 100 kHz offsets = –69 dBc
Low Battery/ RSSI Voltage Measurement
Both the Low Battery (bits 5/23–18) and RSSI (bits
5/17–12) measurement circuits have a 6–bit A/D converter
whose value may be read back via the SPI. The A/D’s sample
their voltages at a frequency equal to the internal SCF clock
frequency divided by 128. The Low Battery Measurement A/D
senses and divides by 2.5 the supply voltage (at Pin 23).
Please note that the minimum Low Battery Detect (LBD)
voltage is 2.7 V, since there is no guarantee that the device will
operate below this value. The RSSI Measurement senses the
voltage at Pin 37.
ARCHIVE INFORMATION
ARCHIVE INFORMATION
Fr
eescale S
emiconduct
or
, I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
nc...