Hybrid transceiver circuit

Details Hybrid transceiver circuit Hybrid transceiver circuit

2000-08-30

2004-10-12

Barnie, Rexford (Department: 2644)

Telephonic communications

Subscriber line or transmission line interface

Hybrid circuit

C379S390040

Reexamination Certificate

active

06804349

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of hybrid circuits of conversion and isolation between a transmission line (for example, a telephone line) and a user equipment or a collective equipment (for example, a telephone exchange or an Internet-type network provider). The present invention more specifically relates to hybrid 2 wire-4 wire circuits that are intended for enabling the sending and receiving of a wanted signal on a same transmission line, and that use a transformer. The function of such hybrid circuits is, in particular, to effect an echo cancellation function to avoid that a signal, extracted towards a receive head, be polluted by an echo coming from a signal transmitted on the line.
2. Discussion of the Related Art
FIG. 1
very schematically shows an example of application of the hybrid circuits to which the present invention applies. This drawing illustrates the connection of different equipment on a telephone line
1
and, more specifically, the connection of equipments on the subscriber side. Line
1
generally is a twin-wire line between a telephone exchange
2
and a connection element
3
on the subscriber side. To simplify, a telephone exchange
2
is considered, but it should be noted that the line transits through different collective equipment such as sub-terminal blocks, terminal blocks, etc. On the subscriber side, connection element
3
may be formed of a separator for branching the telephone line either to a telephone set
4
, or to a modem
5
connected to a digital equipment
6
, for example, a microcomputer. Other configurations than those described hereabove may of course exist on the subscriber side and on the collective system side. However, their detailed discussion would add nothing to the discussion of the present invention and will be accordingly omitted since it is perfectly well known.
Be it on the exchange side or on the subscriber side, the equipment are equipped with a hybrid circuit
7
used as an interface between the telephone line and the high frequency or RF signal processing circuits. Most often, telephone sets are also equipped with hybrid circuits. However, the present invention only applies to circuits intended for carrying data in bands of frequencies greater than speech frequencies.
FIG. 2
schematically shows a hybrid circuit
7
to which the present invention applies. As indicated previously, this circuit is intended for enabling the sending and the receiving of a wanted signal on a same twin-wire line
1
. On the side of line
1
, hybrid circuit
7
includes two inputs/outputs Rx+ and Rx−. On the equipment side, hybrid circuit
7
includes two inputs Tx+ and Tx− intended for receiving a signal to be transmitted on the line, and two outputs E+ and E− intended for giving back a received signal. The inputs and outputs on the equipment side are intended for being connected to heads of transmission and reception of high frequency signals (not shown in FIG.
2
), most often based, for the portion in contact with hybrid circuit
7
, on low-noise amplifier circuits. Both terminals Rx+ and Rx− on the line side are generally formed by the two terminals of a first winding of an isolation transformer, having the terminals of its second winding connected to an impedance matching and echo cancellation circuit enabling conversion towards the 4-wire system on the equipment side. The impedance matching portion has the function of adapting the transformer input on the equipment side with the line impedance. The echo cancellation portion has the function of suppressing, from a received signal sent to outputs E+ and E−, an echo coming from a transmission from terminals Tx+ and Tx− towards terminals Rx+ and Rx−. In a hybrid circuit intended for a transmission-reception of data, it is desired to obtain the smallest possible echo.
The present invention more specifically relates to hybrid circuits intended for the transmission-reception of high frequency signals in separate bands, that is, where the frequency band assigned to the transmission is different from the frequency band assigned to the reception. In such applications, the signals received% and provided by hybrid circuit
7
on terminals E+ and E− are generally filtered (for example, in a high-pass filter for the subscriber side) to improve the echo attenuation.
FIG. 3
shows a conventional example of a hybrid circuit
7
applied to a transmission in separate bands. As previously indicated, the interface between line
1
and an impedance matching and echo cancellation circuit
10
is formed by a transformer
8
, having a first winding
9
(arbitrarily designated as the primary winding) connected to line
1
. In
FIG. 3
, the telephone line has been schematized by its impedance ZL across terminals Rx+ and Rx− of winding
9
of transformer
8
.
On the side of secondary winding
11
, the impedance matching portion of circuit
10
is essentially formed of two resistors Ra, called transmission drive resistors, connecting each terminal Tx+, Tx− to one of terminals A, B of winding
11
. Terminals Tx+ and Tx− correspond to differential output terminals of a high frequency transmission head
12
. Generally, resistors Ra are sized according to the real part of line impedance ZL and to transformation ratio N of transformer
8
. Indeed, transformer
8
most often has a transformation ratio different from one to provide an increase of the voltage level in the transmission direction from the user to the exchange. Generally, Ra=RL/2N
2
, where RL represents the resistance of line impedance ZL.
The echo cancellation function is effected by using the differential structure to extract, from the received signal, the echo of the transmitted signal. For this purpose, each terminal Tx+ and Tx− is connected to the terminal B or A opposite to that to which it is connected by resistor Ra, by means of a series association of two impedances Z
1
and Z
2
. Output terminals E+ and E− of the hybrid circuit are then formed by the respective midpoints of the series associations of impedances Z
1
and Z
2
. Thus, terminal Tx+ is connected to terminal E− by an impedance Z
1
and terminal E− is connected to terminal B by an impedance Z
2
. Terminal Tx− is connected to terminal E+ by an impedance Z
1
and terminal E+ is connected to terminal A by an impedance Z
2
. The transfer function thus obtained enables that the voltage across terminals E+ and E− corresponds to the voltage across terminals A and B, decreased (at least partly) by the transmission voltage across terminals Tx+ and Tx−.
Such an echo cancellation circuit
10
operates properly if line
1
exhibits its characteristic impedance, that is, if it can be assimilated to a resistor. In this case, with Z
1
=
2
Z
2
, a perfect echo cancellation is obtained with purely resistive impedances.
However, the frequency of the received signal (and of the transmitted signal) varies, so that line
1
cannot be assimilated to a pure resistor. Further, the line impedance varies from one line to another, in particular according to the line length. Accordingly, the echo cancellation circuit cannot be formed of resistors only.
In conventional systems, impedances Z
1
and Z
2
are called compromise impedances since they are chosen according to a characteristic batch of telephone lines, generally imposed by telecommunication standards. A compromise sizing of the hybrid circuit is thus performed. The compromise impedances generally have the shapes respectively illustrated in
FIGS. 4A and 4B
, for impedances Z
1
and Z
2
. Impedances Z
1
are formed of a first resistor R
1
in series with a capacitor C
1
, this in parallel with a second resistor R
1
′ (FIG.
4
A). Impedances Z
2
are generally formed of a resistor R
2
in series with a capacitor C
2
(FIG.
4
B).
A first disadvantage of known circuits is that the

Affiliated with

Also associated with

Rating

Hybrid transceiver circuit does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Hybrid transceiver circuit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hybrid transceiver circuit will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3326090