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Appendix A
Digital-to-Analog Converter
Samsung ASIC
A-4
STD130
9. Aperture Jitter
- The sample to sample variation in aperture delay.
10. Bit Error Rate (BER)
- The number of spurious code errors produced for any
given input sine wave frequency at a given clock frequency. In this case it is the
number of codes occurring outside the histogram cusp for a 1/2 FS sine wave.
11. Signal to Noise Ratio
- This signal to noise ratio depends on the resolution
of the converter and automatically includes specifications of linearity, distortion,
sampling time uncertainty, glitches, noise, and settling time. Over half the
sampling frequency, this signal to noise ratio must be specified and should ideally
follow the theoretical formula;
S/N
max
= 6.02N + 1.76dB
3. Phase Locked Loop
1. Lock Time
- The time it takes the PLL to lock onto the system clock. Fast or
slow lock time may be controlled by the loop filter characteristics. The loop filter
characteristics are controlled by varying the R and C components. (Remember
that R and C define the damping-factor as well)
2. Phase Error
- The phase difference between the feedback and the system
clock signal.
3. Clock Jitter
- The deviations in a clock's output transitions from their ideal
positions define the clock jitter. Jitter is sometimes specified as an absolute value
in nanoseconds. All jitter measurement are made at a specified voltage.
1) Cycle-to-Cycle Jitter: The change in a clock's output transition from its
corresponding position in the previous cycle. This kind of jitter is the most difficult
to measure and usually requires a time-interval analyzer.
Figure 1-3.
Cycle-to-Cycle Jitter
The maximum of such values over multiple cycles (J1, J2...) is the max. cycle-to-
cycle jitter.
2) Period Jitter: Period jitter measures the maximum change in a clock's output
transition from its ideal position. You can use period jitter measurements to
calculate timing margins in systems.
Clock
t1
t2
t3
Noise:
jitter J1 = t2
t1
jitter J2 = t3
t2