Datasheet

CLKoutX
CLKoutX*
120:
120:
0.1 PF
0.1 PF
50:Trace
50:
Load
50:
LVPECL
Driver
CLKoutX
CLKoutX*
82:
50:Trace
120:
Load
Vcc
82:
120:
Vcc
LVPECL
Driver
CLKoutX
CLKoutX*
50:
50:Trace
50:
Load
Vcc - 2V
Vcc - 2V
LVPECL
Driver
LMK03000, LMK03000C, LMK03000D, LMK03001
LMK03001C, LMK03001D, LMK03033, LMK03033C
www.ti.com SNAS381O –NOVEMBER 2006–REVISED MARCH 2013
8.7.3 Termination for Single-Ended Operation
A balun can be used with either LVDS or LVPECL drivers to convert the balanced, differential signal into
an unbalanced, single-ended signal.
It is possible to use an LVPECL driver as one or two separate 800 mV p-p signals. When DC coupling one
of the LMK03000 family clock LVPECL drivers, the termination should still be 50 ohms to Vcc - 2 V as
shown in Figure 8-9. Again the Thevenin equivalent circuit (120 Ω resistor connected to Vcc and an 82 Ω
resistor connected to ground with the driver connected to the junction of the 120 Ω and 82 Ω resistors) is a
valid termination as shown in Figure 8-10 for Vcc = 3.3 V.
Figure 8-9. Single-Ended LVPECL Operation, DC Coupling
Figure 8-10. Single-Ended LVPECL Operation, DC Coupling, Thevenin Equivalent
When AC coupling an LVPECL driver use a 120 Ω emitter resistor to provide a DC path to ground and
ensure a 50 ohm termination with the proper DC bias level for the receiver. The typical DC bias voltage for
LVPECL receivers is 2 V (See Section 8.7.2). If the other driver is not used it should be terminated with
either a proper AC or DC termination. This latter example of AC coupling a single-ended LVPECL signal
can be used to measure single-ended LVPECL performance using a spectrum analyzer or phase noise
analyzer. When using most RF test equipment no DC bias (0 V DC) is expected for safe and proper
operation. The internal 50 ohm termination the test equipment provides correctly terminates the LVPECL
driver being measured as shown Figure 8-11. When using only one LVPECL driver of a
CLKoutX/CLKoutX* pair, be sure to properly terminate the unused driver.
Figure 8-11. Single-Ended LVPECL Operation, AC Coupling
Copyright © 2006–2013, Texas Instruments Incorporated Application Information 35
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LMK03033C