Mux output option ph0 ph1 – Achronix Speedster22i Memory PHY User Manual
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UG043, April 26, 2014
The MDLL uses a regulated supply generated by a high performance on-board regulator to
achieve the best possible performance in terms of jitter. It gets a clock as its reference to
generate desired delay in its delay cells. The delay cells used in its VCDL is based on a
current starved technique to provide the delay to generate the feedback signal. The phase of
the feedback signal is compared with the reference signal. This phase difference is translated
to voltage (PBIAS and NBIAS) by the phase detector and charge pump, which is given back
to the VCDL block to generate the required delay by either pushing out or pulling in the
feedback clock to reduce the phase error between the reference clock and the feedback clock.
The VCDL has 16 delay elements, and each delay cell provides 22.5 deg phase difference in
locked condition. As there are 16 delay cells in series, the out signal of the 16th delay cell will
have a 360 degrees phase offset with respect to the reference clock. Figure 11 below shows a
block diagram of the MDLL.
Delay Cell Block
ph360
Start-up
Phase detector
Charge Pump
Bias Generator
L
o
o
p
F
ilt
e
r
ph0
up
dn
Openloop_sel
Master
enable
PLL CLK
Front
buffer
16
th
Delay
cell
1
st
Delay
cell
Load
buffer
ph0
ph45
ph90
ph135
ph180
ph225
ph270
ph315
Pbias
Nbias
Figure 11: MDLL Block Diagram
The SDLL and the phase interpolator are used to adjust the delay of the strobe signal and
data signals in the data module so that they will be aligned. The phase interpolator gets 17
clocks with a phase separation of 22.5 degrees from the SDLL, and then performs fine tuning
by mixing various phases as determined by the programmable config bit settings. The phase
interpolator has two stages of mixing the clock. In the first stage it performs coarse tuning
through a mux by selecting the ph0 and ph1 option list as shown in Table 6.
Table 6: Phase Interpolator Mux Output List
Mux Output Option
Ph0
Ph1
1
0
22.5
2
22.5
45
3
45
67.5
4
67.5
90
5
90
112.5
6
112.5
135
7
135
157.5
8
157.5
180