Rainbow Electronics DS3150 - Manual (Page 12)

DS3150
12 of 22
JITTER ATTENUATOR
The DS3150 contains an onboard jitter attenuator that can be placed in either the receive path or the
transmit path or disabled. This selection is made through the RMON and TTS* input signals. See Table
1H for selection details. Figure 1H shows the minimum jitter attenuation for the device when the jitter
attenuator is enabled. Figure 1H also shows the receive jitter transfer when the jitter attenuator is
disabled.
The jitter attenuator consists of a narrowband PLL to retime the selected clock, a 16x2-bit FIFO to buffer
the associated data while the clock is being retimed, and logic to prevent over/underflow of the FIFO in
the presence of very large jitter amplitudes. The PLL requires a stable, accurate clock on MCLK (or on
TCLK if MCLK is tied high or left floating). It has a loop bandwidth of MCLK/2058874 (see corner
frequencies in Figure 1H), and attenuates jitter at frequencies higher than the loop bandwidth while
allowing jitter (and wander) at lower frequencies to pass through relatively unaffected.
Table 1H. RMON AND TTS* SIGNAL DECODE
RMON TTS* RECEIVE 20dB
FLAT GAIN
TRANSMIT LINE
DRIVER
JITTER ATTENUATOR
0 0 Disabled Three-stated Disabled
0 1 Disabled Enabled Disabled
0 Float Disabled Enabled Enabled in Tx Path
1 0 Enabled Three-stated Disabled
1 1 Enabled Enabled Disabled
1 Float Enabled Enabled Enabled in Tx Path
Float 0 Disabled Three-stated Enabled in Rx Path
Float 1 Disabled Enabled Enabled in Rx Path
Float Float Disabled Enabled Enabled in Rx Path
Figure 1H. DS3150 JITTER ATTENUATION/JITTER TRANSFER
10 100 1k 10k 100k 1M
21.7Hz (T3)
16.7Hz (E3)
25.2Hz (STS-1) 1k
-30
-20
-10
E3 [TBR24 (1997)]
Frequency (Hz)
0
T3 [GR-499 (1995)]
Category I DS3150
Typical
Receiver Jitter
Transfer with
Jitter Attenuator
Disabled
200k
DS3150
T3 / E3 / STS-1
Minimum Jitter
Attenuation with
Jitter Attenuator
Enabled
40Hz
T3 [GR-253 (1999)]
Category I
27Hz
STS-1
[GR-253 (1999)]
Category II
40k 59.6k
T3 [GR-499 (1999)]
Category II
J
itter At
ten
uat
ion
(dB)