Test and Measurement Setup, Signal Waveforms

CY24272

Test and Measurement Setup

Swing Current Control

ISET

RRC

Figure 3. Clock Outputs

	VTS			Measurement
	VTS			Point V	T
					T
CLK		R1	ZCH		RT1
CLK	R2	R3 CS			RT2
	R2	R3 CS			RT2

Differential Driver

	VTS			Measurement	V
	VTS			Point	V	T
						T
CLKB		R1	ZCH			RT1
CLKB	R2	R3 CS				R
	R2	R3 CS				R	T2
							T2

Example External Resistor Values

and Termination Voltages for a 50Ω Channel

Parameter	Value	Unit
R1	33.0	Ω
R2	18.0	Ω
R3	17.0	Ω
RT1	60.4	Ω
RT2	301	Ω
CS	2700	pF
RRC	432	Ω
VTS	2.5V	V
VT	1.2V	V

Signal Waveforms

A physical signal that appears at the pins of a device is deemed valid or invalid depending on its voltage and timing relations with other signals. Input and output voltage waveforms are defined as shown in Figure 4 on page 11. Both rise and fall times are defined between the 20% and 80% points of the voltage swing, with the swing defined as VH–VL.

Figure 5 on page 11 shows the definition of the output crossing point. The nominal crossing point between the complementary outputs is defined as the 50% point of the DC voltage levels. There are two crossing points defined: Vx+ at the rising edge of CLK and Vx– at the falling edge of CLK. For some waveforms, both Vx+ and Vx– are below Vx,nom (for example, if tCR is larger than tCF).

Jitter

This section defines the specifications that relate to timing uncer- tainty (or jitter) of the input and output waveforms. Figure 6 on page 11 shows the definition of cycle-to-cycle jitter with respect to the falling edge of the CLK signal. Cycle-to-cycle jitter is the difference between cycle times of adjacent cycles. Equal require- ments apply rising edges of the CLK signal. Figure 7 on page 11 shows the definition of cycle-to-cycle duty cycle error (tDC,ERR). Cycle-to-cycle duty cycle is defined as the difference between tPW+ (high times) of adjacent differential clock cycles. Equal requirements apply to tPW-, low times of the differential click cycles.

Notes

19.Max and min output clock cycle times are based on nominal outputs frequency of 300 and 667 MHz, respectively. For spread spectrum modulated differential or single-ended REFCLK, the output clock tracks the modulation of the input.

20.Output short term jitter spec is the absolute value of the worst case deviation.

21.tSKEW is the timing difference between any two of the four differential clocks and is measured at common mode voltage. ΔtSKEW is the change in tSKEW when the operating temperature and supply voltage change.

22.tCR,CF applies only when appropriate RRC and output resistor network resistor values are selected to match pull up and pull down currents.

Document Number: 001-42414 Rev. **

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