Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2002-03-04
2003-04-29
Chan, Jason (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C250S201100
Reexamination Certificate
active
06556330
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an integrated photodiode and infrared receiver circuit.
2. Description of the Related Art
Infrared wireless data communication is a useful method for short range (in the approximate range of 0-10 meters) wireless transfer of data between electronic equipment; such as, cellular phones, computers, computer peripherals (printers, modems, keyboards, cursor control devices, etc.), electronic keys, electronic ID devices, and network equipment. Infrared wireless communication devices typically have the advantages of smaller size, lower cost, fewer regulatory requirements, and a well defined transmission coverage area as compared to radio frequency wireless technology (i.e. the zone of transmission is bounded by physical walls). In addition, infrared wireless communication has further advantages with regard to reliability, electro-magnetic compatibility, multiplexing capability, easier mechanical design, and convenience to the user as compared to cable based communication technology. As a result, infrared data communication devices are useful for replacing 0-10 meter long data transfer cables between electronic devices, provided that their size and costs can be reduced to that of comparable cable technology. As examples of the type of wireless communications links that are presently in use, the Infrared Data Association (IrDA) Physical Layer Link Specification 1.1e specifies two main physical layer infrared modulation protocols.
The IrDA Physical Layer Link Specification 1.1e also specifies two modes for modulation of data on the infrared transmitted signal. One mode is a low-speed (2.4 Kbp/s to 115 Kbp/s) on-off infrared carrier using asynchronous modulation where the presence of a pulse indicates a 0 bit and the absence of a pulse indicates a 1 bit. The second mode is a high speed (576 Kbp/s to 4 Mb/s) synchronous Four Pulse Position Modulation (4PPM) method in which the time position of a 125 nS infrared pulse in a 500 nS frame encodes two bits of information. The 1.1e specification also specifies a preamble pattern which is sixteen repeated transmissions of a predetermined set of symbols.
Infrared data communications devices typically consist of transmitter and receiver components. The infrared data transmitter section consists of one or more infrared light emitting diodes (LEDs), an infrared lens, and an LED current driver. A conventional infrared data receiver typically consists of an infrared photodiode and a high gain receiver amplifier with various signal processing functions, such as automatic gain control (AGC), background current cancelling, filtering, and demodulation. For one-directional data transfer, only a transmitter at the originating end and a receiver at the answering end is required. For bi-directional communication, a receiver and transmitter at each end is required. A combined transmitter and receiver is called a transceiver.
A representative example of a conventional infrared data transmitter and receiver pair is shown in FIG.
1
A. Infrared transmitter
10
includes LED
16
which generates a modulated infrared pulse in response to transistor
14
being driven by the data signal input at D
IR
. The modulated infrared signal is optically coupled to an infrared detector, such as photodiode
24
normally operated in current mode (versus voltage mode) producing an output current which is a linear analog of the optical infrared signal falling on it. The infrared pulses generated by LED
16
strike photodiode
24
causing it to conduct current responsive to the data signal input at D
IR
thereby generating a data signal received at D
IR
.
In receiver
20
, the signal received at D
IR
is transformed into a voltage signal V
IR
and amplified by amplifier
26
. The signal output from amplifier
26
then feeds into comparator
42
which demodulates the received signal by comparing it to a detection threshold voltage V
DET
in order to produce a digital output data signal at D
OUT
.
The received signal waveform will have edges with slope and will often include a superimposed noise signal. As a result, V
DET
is ideally placed at the center of the received signal waveform so that the output data signal has a consistent waveform width despite the slope of the received signal edges. Also, placing V
DET
at the center of the received signal improves the noise immunity of receiver
20
because the voltage difference between V
DET
and both the high and low levels of the received signal is maximized such that noise peaks are less likely to result in spurious transitions in D
OUT
.
The received signal, however, can vary in amplitude by several orders of magnitude due primarily to variations in the distance between transmitter
10
and receiver
20
. The strength of the received signal decreases proportional to the square of the distance. Depending on the range and intensity of the infrared transmitter, the photodiode outputs signal current in the range of 5 nA to 5 mA plus DC and AC currents arising from ambient infrared sources of sunlight, incandescent and fluorescent lighting. As a consequence, the center of the received signal waveform will vary, whereas V
DET
must generally be maintained at a constant level. To address this problem, receivers typically include an automatic gain control (AGC) mechanism to adjust the gain responsive to the received signal amplitude. The received signal is fed to AGC peak detector
36
which amplifies the signal and drives current through diode
32
into capacitor
28
when the signal exceeds the AGC threshold voltage V
AGC
in order to generate a gain control signal. The gain control signal increases in response to increasing signal strength and correspondingly reduces the gain of amplifier
26
so that the amplitude of the received signal at the output of amplifier
26
remains relatively constant despite variations in received signal strength.
At a minimum, infrared receiver
20
amplifies the photodetector signal current and then level detects or demodulates the signal when it rises above the detect threshold V
DET
thereby producing a digital output pulse at D
OUT
. For improved performance, the receiver may also perform the added functions of blocking or correcting DC and low frequency AC ambient (1-300 uA) signals and Automatic Gain Control (AGC) which improves both noise immunity and minimizes output pulse width variation with signal strength.
The structure of the conventional discrete PIN photodiode
24
is illustrated in
FIG. 1B. A
wafer
50
is lightly doped with N dopant in order to produce an intrinsic region
56
. A P+ region
52
is formed on one surface of the wafer and an N+ region
58
is formed on the opposing surface of wafer
50
with intrinsic region
56
interposed P+ region
52
and N+ region
58
. A reflective layer
60
, typically gold, is disposed on the surface containing P+ region
58
with reflective layer
60
also serving as the electrical contact to N+ region
58
. A metal contact
54
is disposed on the surface containing P+ region
52
to provide the electrical connection to the P+ region.
Typically, one power supply potential is applied to the reflective layer
60
and another power supply voltage is applied to contact
54
to reverse bias the PN junction formed by P+ region
52
and N+ region
18
. This forms a depletion region within the intrinsic region
56
wherein electron and hole charge carrier pairs generated by light photons incident upon the intrinsic region
56
are rapidly accelerated toward the P+ and N+ regions respectively by the electric field of the reverse bias voltage. Charge carrier pairs are also typically generated outside the depletion region within intrinsic region
56
which diffuse, due to random thermal motion of the carriers, at a much slower velocity until they reach either the depletion region or the junction formed by P+ region
52
and intrinsic region
56
of photodiode
24
.
A conventional photodiode that is designed for h
Bello Agustin
Chan Jason
Francissen Vernon W.
Gardner Carton & Douglas LLC
Integration Associates Inc.
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