Differential envelope detector

Details Differential envelope detector Differential envelope detector

2000-08-10

2003-05-20

Lam, Tuan T. (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Specific signal discriminating without subsequent control

By amplitude

C327S054000, C327S062000

Reexamination Certificate

active

06566915

ABSTRACT:

FIELD
The present invention relates to analog circuits, and more particularly, to envelope detectors.
BACKGROUND
The Home Phoneline Networking Alliance (HomePNA) is an incorporated, non-profit association of companies working to bring networking technology to the home. See www.homepna.org. HomePNA envisions bringing Ethernet technology to the home by utilizing existing home phone wiring for the network physical medium. HomePNA provides specifications for the physical layer (PHY), its interface to an Ethernet MAC (Media Access Control), and its interface to the home phone wiring. See the IEEE (Institute of Electrical and Electronic Engineers) 802.3 standard for Ethernet.
The position of a HomePNA PHY in relationship to the OSI (Open Systems Interconnection) model is illustrated in FIG.
1
. Logical Link Control (LLC)
102
and MAC
104
are implemented in accordance with IEEE 802.3, and HomePNA PHY
106
communicates with MAC
104
via interface
108
. Additional sublayers, and other optional layers, may be added to the layers shown in
FIG. 1
so that PHY
106
may provide services to other communication protocols, such as Gigabit Ethernet. In practice, PHY
106
and MAC
104
may be integrated on a single die, so that interface
108
is not readily visible.
PHY
106
receives a MAC frame from MAC
104
, strips off the 8 octets of preamble and delimiter from the MAC frame, adds a HomePNA PHY header to form a HomePNA PHY frame, and transmits the PHY frame on physical medium
108
. A PHY frame is transmitted on physical medium
108
utilizing pulse position modulation (PPM). All PHY symbols transmitted on physical medium
108
comprise a pulse formed of an integer number of cycles of a square wave that has been filtered with a bandpass filter. The position of the pulse conveys the transmitted symbol. Differential signaling is employed, in which a pulse and its negative are transmitted on two wires for each transmitted symbol.
FIG. 2
illustrates an example of received waveforms. Although differential signaling is employed, for simplicity
FIG. 2
shows only a single-ended version of the received differential signal. Each symbol is 129 tics long, where 1 tic is defined as (7/60)10
−6
seconds, which is approximately 116.667 nanoseconds. Pulses are positioned within one of four time slots to convey two bits of information. The time slots are separated by 20 tics, and are at positions
66
,
86
,
106
, and 126 tics from the beginning of a symbol interval. A special SYNC symbol, indicated as AID (Access Identification) symbol
0
in
FIG. 2
, is composed of a SYNC_START pulse beginning at tic=0 and a SYNC_END pulse beginning at tic=126. In
FIG. 2
, AID symbol
1
comprises a pulse in position
1
(tic=86), and AID symbol
2
comprises a pulse at position
2
(tic=106). A receiving PHY performs full-wave rectification of the received signals, and compares the envelope of the rectified signals with an AID slice threshold. The PHY detects a received pulse if its envelope exceeds the AID slice threshold. As soon as a pulse is detected by a PHY, the PHY disables further indications of detection until a time AID_END_BLANK (located at tic=61) from the beginning of the pulse, after which detection indication must be re-enabled for the next received pulse.
One approach for detecting the envelope of a differential signal is to form the difference of the received differential signals to provide a single-ended signal, followed by detecting the envelope of the single-ended signal. One such envelope detector is shown in
FIG. 3. A
single-ended voltage signal V is applied to non-inverting port
302
of differential amplifier
304
and to inverting port
306
of differential amplifier
308
. Diodes
310
and
312
provide full-wave rectification, so that capacitor
314
charges when either diode
310
or diode
312
is forward biased. The output voltage V
out
at node
316
is proportional to the envelope of the input signal V. Resistor
318
allows capacitor
314
to discharge when there is no received signal.
The present invention improves upon the envelope detector of
FIG. 3
for networks employing differential signaling.


REFERENCES:
patent: 5206602 (1993-04-01), Baumgartner et al.
patent: 5982232 (1999-11-01), Rogers
patent: 6011435 (2000-01-01), Takeyabu et al.

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