Bel Fuse Inc. 198 Van Vorst Street, Jersey City, NJ 07302 • Tel 201-432-0463 • Fax 201-432-9542 • www.belfuse.com

HIGH FREQUENCY MAGNETICS

©2000 Bel Fuse Inc.

Specifications subject to change without notice. 07.00

TM00145B

Application Note for Miniature Pulse Transformers

T1-105

Two-Transformer Design and Common Termination Network

A typical line termination network using the 2795T transformer for the receive interface and

the 2795Y transformer for the transmit interface is shown below for a single channel. The

termination network consists of capacitors and resistors arranged to provide the proper voltage

gain and impedance matching to the characteristic impedance of the various transmission lines.

The network is designed to operate with both E1 cable impedances (75

Ω and 120Ω) with no

change in components. For DS1 applications (100

Ω), only the resistor values need to be changed.

The 2795T transformer is used for all three cable impedances at the receive interface. The 2795Y

transformer is used for all three cable impedances at the transmit interface. Figure 2 below shows

the proper connections for each cable impedance. Connections for cable selection are made on

the line side for both receive and transmit interfaces. The components and suggested values

are listed in Table 2. Capacitor CS provides high-frequency return loss enhancement.

2795T and 2795Y Transformers Application Note

Figure 2. Connections for one 2795T transformer and one 2795Y transformer

2

2795Y

Transformer

Transmit Data

RT

RT

4

(Line)

Device

(1 Channel)

RTIP

RRING

TTIP

TRING

RR

CC

2795T

Transformer

Receive Data

RR

3

1

4

(Line)

RS

75

120

100

5

2

6

T1

T2

1

5

120

100

75

CS

3

6