Differential voltage transmission circuit

Details Differential voltage transmission circuit Differential voltage transmission circuit

2003-05-22

2004-08-17

Nguyen, Long (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Specific signal discriminating without subsequent control

By amplitude

C327S066000, C327S067000, C327S108000, C327S379000

Reexamination Certificate

active

06777983

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a differential voltage transmission circuit. In particular, the present invention relates to a differential voltage transmission circuit with adjustable reference current.
2. Description of the Related Art
FIG. 1
shows a conventional differential voltage transmission circuit. The conventional differential voltage transmission circuit comprises a bandage reference circuit
10
to provide a bandgap bias V
bg
. The reference current I
ref
is generated by the bandgap bias V
bg
and the external resistor R
ext
. Next, the reference current I
ref
is output to transmitter
12
. The transmitter
12
comprises an external termination resistor R
term
. When the reference current I
ref
flows through the external termination resistor R
term
, a first output voltage V
op
and a second output voltage V
on
are generated at both terminals of the termination resistor R
term
, then the output voltage V
o
is generated, that is, the difference between the first output voltage V
op
and the second output voltage V
on
.
Because the reference current I
ref
is influenced by the external resistor R
ext
, the value of the external resistor R
ext
must be very exact to avoid influencing the reference current I
ref
. Thus, the external resistor R
ext
is fabricated by another factory, after confirming the actual resistance, then the external resistor R
ext
is set on the circuit board to generate an exact reference current I
ref
.
However, the circuit board must add via holes to set up the external resistor R
ext
. The additional external resistor R
ext
and via holes, however, increase costs and complicate the fabricating process.
To solve the cost problem, the external resistor R
ext
is replaced with an internal resistor formed with the bandage reference circuit
10
by CMOS process. Thus, the cost of the external resistor R
ext
is economized. However, errors with the internal resistor formed by CMOS process are increased to as much as ±30%, which cannot provide a demanding reference current.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a differential voltage transmission circuit that provides the reference current by adjustment without using the external resistor.
To achieve the above-mentioned object, the differential voltage transmission circuit comprises a reference bias circuit, a differential comparator, a decision circuit, and an output driving circuit. The reference bias circuit outputs a first reference voltage, a second reference voltage and a reference current corresponding to a reference current adjusting signal. The differential comparator compares the difference between the first reference voltage and the second reference voltage with the difference between a first output voltage and a second output voltage, and outputs a result signal corresponding to the compared result. The decision circuit outputs the reference current adjusting signal corresponding to the result signal. The output circuit outputs the first output voltage and the second output voltage generated at both terminals of a termination resistor when the reference current flows through the termination resistor.


REFERENCES:
patent: 6097245 (2000-08-01), Dobbelaere et al.
patent: 6111431 (2000-08-01), Estrada
patent: 6590436 (2003-07-01), Jordanger et al.
patent: 6650149 (2003-11-01), Wong

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