SL1461SA
VCO STABILITY vs TEMP and SUPPLY
480
479.5
479
SUPPLY (V)
4.5
4.75
5
5.25
5.5
FREQUENCY (MHz)
478.5
478
477.5
477
476.5
476
475.5
–20
5
30
TEMP/°C
55
80
Fig.8 SL1461SA VCO centre frequency uncompensated temperature stability
2.0
1.5
AGC
OUTPUT 1.0
VOLTAGE
AGC BIAS RESISTOR 5.1K
AGC BIAS CURRENT 297 A
AGC LOAD RESISTOR 3.9K
AGC BIAS RESISTOR 10.5K
AGC BIAS CURRENT 150 A
AGC LOAD RESISTOR 4.7K
AGC BIAS RESISTOR 32K
AGC BIAS CURRENT 52 A
AGC LOAD RESISTOR 10K
0.5
–70
–60
–50
–40
–30
–20
–10
0
V
CC
= 5.0 VOLTS
RF INPUT LEVEL (dBm) UNMODULATED
Fig.9 SL1461SA AGC output voltage for differing values of AGC bias resistor
APPLICATION NOTES
Capture range
Under conditions when there is no RF input signal present,
the SL1461SA may react to spurious radiation from the free
running oscillator coupling into the RF inputs. Because of the
constant phase error between the VCO input to the phase
detector and the spuriously coupled signal via the RF input, the
phase comparator will drive the control voltage to either the
bottom or the top of the range.
In such a case, the capture range will be asymmetrical
about the VCO free running frequency, since any control
voltage will only be able to tune the VCO in one direction if the
tuning voltage is already at the max or min.
This effect can be avoided by driving the RF input
differentially or achieving good common mode rejection to the
VCO signal.
The lock range is independant of the above effects and will
be symmetric about the centre of the phase detector S-curve
provided the VCO is correctly aligned.
EXAMPLE
Loop out of lock
Tuning voltage =4.3V (maximum)
frequency =520MHz (maximum
It is only possible to capture signals below this frequency since
the VCO is already at its maximum frequency.
Testing of capture range should be done with the device
operating under normal conditions. An input signal of between
-35dBm to -10dBm is suitable for such a measurement.
9
MITEL [ MITEL NETWORKS CORPORATION ]
