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CDCM6208V1FRGZR Datasheet(PDF) 63 Page - Texas Instruments
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CDCM6208V1FRGZR Datasheet(HTML) 63 Page - Texas Instruments
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SCAS943 – MAY 2015
Figure 46. CDCM6208V1F PLL Loop Filter Topology
Loop Filter Component Selection
The loop filter setting and external resistor selection is important to set the PLL to best possible bandwidth and to
minimize jitter. A high bandwidth (
≥ 100 kHz) provides best input signal tracking and is therefore desired with a
clean input reference (synthesizer mode). A low bandwidth (
≤ 1 kHz) is desired if the input signal quality is
unknown (jitter cleaner mode). TI provides a software tool that makes it easy to select the right loop filter
components. C1, R2, and C2 are external loop filter components, connected to the ELF pin. The 3
pole of the
loop filter is device internal with R3 and C3 register selectable.
Device Output Signaling
LVDS-like: All outputs Y[7:0] support LVDS-like signaling. The actual output stage uses a CML structure and
drives a signal swing identical to LVDS (~350mV). The output slew rate is faster than standard LVDS for best
jitter performance. The LVDS-like outputs should be AC-coupled when interfacing to a LVDS receiver. See
reference schematic Figure 64 for an example. The supply voltage for outputs configured LVDS can be selected
freely between 1.8 V and 3.3 V.
LVPECL-like: Outputs Y[3:0] support LVPECL-like signaling. The actual output stage uses a CML structure but
drives the same signal amplitude and rise time as true emitter coupled logic output stages. The LVPECL-like
outputs should be AC-coupled, and contrary to standard PECL designs, no external termination resistor to VCC-
2V is used (fewer components for lowest BOM cost). See reference schematic Figure 64 for an example. The
supply voltage for outputs configured LVPECL-like is recommended to be 3.3 V, though even 1.8 V provides
nearly the same output swing and performance at much lower power consumption.
CML: Outputs Y[3:0] support standard CML signaling. The supply voltage for outputs configured CML can be
selected freely between 1.8 V and 3.3 V. A true CML receiver can be driven DC coupled. All other differential
receiver should connected using AC coupling. See reference schematic Figure 64 for a circuit example.
HCSL: Outputs Y[7:4] support HCSL signaling. The supply voltage for outputs configured HCSL can be selected
freely between 1.8 V and 3.3 V. HCSL is referenced to GND, and requires external 50
Ω termination to GND.
See reference schematic for an example.
CMOS: Outputs Y[7:4] support 1.8 V, 2.5 V, and 3.3 V CMOS signaling. A fast or reduced slew rate can be
selected through register programming. Each differential output port can drive one or two CMOS output signals.
Both signals are “in-phase”, meaning their phase offset is zero degrees, and not 180
˚. The output swing is set by
providing the according supply voltage (for example, if VDD_Y4=2.5 V, the output swing on Y4 will be 2.5 V
CMOS). Outputs configured for CMOS should only be terminated with a series-resistor near the device output to
preserve the full signal swing. Terminating CMOS signals with a 50
Ω resistor to GND would reduce the output
signal swing significantly.
Copyright © 2015, Texas Instruments Incorporated
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