XR-2212_06 Datasheet, PDF (9/20 Pages) Exar Corporation – Precision Phase-Locked Loop

XR-2212
current drawn from Pin 12 must be limited to <3 mA for
proper operation of the circuit.
VCO Timing Capacitor (Pins 13 and 14): VCO frequency
is inversely proportional to the external timing capacitor,
C₀, connected across these terminals (see Figure 6). C₀
must be nonpolar, and in the range of 200pF to 10mF.
VCO Quadrature Output (Pin 15): The low-level ([
0.6Vpp) output at this pin is at quadrature phase (i.e. 90°
phase-offset) with the other VCO outputs at Pins 3 and 5.
The DC level at Pin 15 is approximately 300mV above
V_REF. The quadrature output can be used with an external
multiplier as a “lock detect” circuit. In order not to degrade
oscillator performance, the output at Pin 15 must be
buffered with an external high impedance low
capacitance amplifier. When not in use, Pin 15 should be
left open-circuited.
Phase Detector Input (Pin 16): Voltage output of the
VCO (Pin 5) or the output of an external frequency divider
is connected to this pin. The DC level of the sensing
threshold for the phase detector is referenced to V_REF. If
the signal is capacitively coupled to Pin 16, then this pin
must be biased from Pin 11, through an external resistor,
R_B (R_B [ 10kW). The peak voltage swing applied to Pin
16 must not exceed (V_CC - 1.5) volts.
PHASE-LOCKED LOOP PARAMETERS
Transfer Characteristics
Figure 10 shows the basic frequency to voltage
characteristics of XR-2212. With no input signal present,
filtered phase detector output voltage is approximately
equal to the internal reference voltage, V_REF at Pin 11.
The PLL can track an input signal over its tracking
bandwidth, shown in the figure. The frequencies f_TL and
f_TH represent the lower and the upper edge of the tracking
range, f₀ represents the VCO center frequency.
Tracking
2V_R
Bandwidth
Df
Df
V_R
0
f_TL
f_O
f_TH
Frequency
Input Signal Frequency
Figure 10. Phase Detector Output Voltage (Pin 10) as a Function of Input Signal Frequency
Note
Output Voltage is Referenced to Internal Reference Voltage V_REF at Pin 11
Rev. 2.10
9