Browse Prior Art Database

CCITT V35 Balanced Driver With a Single Power Supply

IP.com Disclosure Number: IPCOM000120403D
Original Publication Date: 1991-Apr-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 58K

Publishing Venue

IBM

Related People

Braquet, H: AUTHOR [+3]

Abstract

Disclosed is a circuit which performs the functions of a CCITT V35 driver for balanced interchange circuits and uses a single + Vcc power supply, typically +5 volts.

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This is the abbreviated version, containing approximately 64% of the total text.

CCITT V35 Balanced Driver With a Single Power Supply

      Disclosed is a circuit which performs the functions of a
CCITT V35 driver for balanced interchange circuits and uses a single
+ Vcc power supply, typically +5 volts.

      As shown in Fig. 1, the basic circuit is made of two CMOS
inverters, M1, M2. The data to be transmitted is fed to the input of
the first inverter M1, the output of which is connected to the
resistor R1 of the V35 terminator and to the input of the second
inverter M2. The output of M2 is connected to the resistor R2 of the
V35 terminator. The other ends of resistors R1 and R2 are connected
to the output V35 ports A and B. A third resistor R3 is connected to
the output ports A and B.  Besides, R1 =  R2 = R.

      The circuit of Fig. 1 fulfills the V35 driver recommendations
except for the mean voltage of A and B with respect to Ground, also
called DC offset. The V35 recommendation for this parameter is 0.6
volts maximum, while the circuit, as described, gives to this
parameter a value of + Vcc/2 which is equal to 2.5 volts.

      Disclosed is a means to lower this DC offset value down to +0.6
volt, while keeping a single power supply + Vcc. As shown in Fig. 2,
a current source referenced to the Ground is used to sink a defined
current from a center tap on the resistor R3. Thus, the DC voltage at
this center tap CT is brought down to 0.6 volt or less.

      Two implementations of the circuits are shown in Figs. 3A and
3B.

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