DS2155 Monitor Mode Design

Abstract: Application note 400 describes how to connect the Dallas Semiconductor DS2155 single chip transceivers (SCTs) in a monitor mode interface. In monitor mode, the T1/E1 line is tapped by a secondary receive circuit to monitor the data flow. In monitor mode, a pair of resistors are used to split the signal from the main T1/E1 line to the monitor path. While there is an insignificant drop in the signal level of the main T1/E1 line, the monitor path can be orders of magnitude lower than the original signal. To compensate for the signal loss, the transformer winding can be altered or the receiver can integrate an active linear (flat) gain amplifier. Either of these methods will provide an additional signal boost. To simplify the external receive circuit design, the DS2155 was created with integrated linear-gain amplifiers. This application note contains the general overview of the monitor mode application and also the specifics on how to properly design and program the DS2155.