DS2154 datasheet(64/87 Pages) DALLAS

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DS2154

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Normally, the clock that is output at the RCLKO pin is the recovered clock from the E1 AMI/HDB3

waveform presented at the RTIP and RRING inputs. When no AMI signal is present at RTIP and RRING,

a Receive Carrier Loss (RCL) condition will occur and the RCLKO will be sourced from the clock

applied at the MCLK pin. If the jitter attenuator is either placed in the transmit path or is disabled, the

RCLKO output can exhibit slightly shorter high cycles of the clock. This is due to the highly oversampled

digital clock recovery circuitry. If the jitter attenuator is placed in the receive path (as is the case in most

applications), the jitter attenuator restores the RCLK to being close to 50% duty cycle. Please see the

Receive AC Timing Characteristics in Section 14 for more details.

12.2 TRANSMIT WAVESHAPING AND LINE DRIVING

The DS2154 uses a set of laser-trimmed delay lines along with a precision Digital-to-Analog Converter

(DAC) to create the waveforms that are transmitted onto the E1 line. The waveforms created by the

DS2154 meet the ITU G.703 specifications. See Figure 12-3. The user will select which waveform is to

be generated by properly programming the L2/L1/L0 bits in the Line Interface Control Register (LICR).

The DS2154 can be set up in a number of various configurations depending on the application. See Table

12-2 and Figure 12-1.

LINE BUILD OUT SELECT IN LICR Table 12-2

LLL

210

APPLICATION

TRANSFORMER

RETURN

LOSS

RT (SEE

FIGURE 12-1)

000

75 ohms normal (See Note 1)

1:1.15 step-up

0 ohms

001

120 ohms normal

1:1.15 step-up

0 ohms

010

75 ohms w/ protection resistors

1:1.15 step-up

8.2 ohms

011

120 ohms w/ protection resistors

1:1.15 step-up

8.2 ohms

100

75 ohms w/ high return loss

1:1.15 step-up

21dB

27 ohms

110

75 ohms w/ high return loss

1:1.36 step-up

21dB

18 ohms

100

120 ohms w/ high return loss

1:1.36 step-up

21dB

27 ohms

NOTE:

1. This LBO is not recommended for use in the A2 revision of the DS2154.

Due to the nature of the design of the transmitter in the DS2154, very little jitter (less then 0.005 UIpp

broadband from 10 Hz to 100 kHz) is added to the jitter present on TCLK. Also, the waveforms that they

create are independent of the duty cycle of TCLK. The transmitter in the DS2154 couples to the E1

transmit shielded twisted pair or COAX via a 1:1.15 or 1:1.36 step up transformer as shown in Figure 12-

1. In order for the devices to create the proper waveforms, this transformer used must meet the

specifications listed in Table 12-3 The line driver in the DS2154 contains a current limiter that will

prevent more than 50 mA (rms) from being sourced in a 1 ohm load.

TRANSFORMER SPECIFICATIONS Table 12-3

SPECIFICATION

RECOMMENDED VALUE

Turns Ratio

1:1 (receive) and 1:1.15 or 1:1.36 (transmit)

± 5%

Primary Inductance

600 uH minimum

Leakage Inductance

1.0 uH maximum

Intertwining Capacitance

40 pF maximum

DC Resistance

1.2 ohms maximum

DS2154 Datasheet(PDF) 64 Page - Dallas Semiconductor

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