Infrared repeater

An IR repeater is disclosed which is resistant to CFL interference. The IR repeater includes a receiver section for receiving an IR light signal representing a coded signal modulated by a modulating signal, and for detecting the coded signal. An oscillator generates a transmitter modulating signal, and a transmitter section, coupled to the receiver section and the oscillator, generates an IR light signal representing the detected coded signal modulated by the transmitter modulating signal.

FIELD OF THE INVENTION 
The present invention relates to an infrared repeater, and more 
specifically an infrared repeater which remains operative in the presence 
of interference caused by compact fluorescent lights. 
BACKGROUND OF THE INVENTION 
Current wireless remote control units for consumer electronic equipment, 
such as television receivers, video cassette recorders, and cable or 
satellite receiver boxes, operate by transmitting an infrared (IR) light 
signal, representing a coded signal modulated on a modulating signal, from 
the remote control unit to the consumer electronic equipment. This 
modulated IR light signal is received by an IR receiver in the consumer 
electronic equipment, demodulated, decoded, and the appropriate action 
taken. IR remote control units are line-of-sight devices, meaning that any 
consumer electronic equipment which is in a shadow with respect to the IR 
light generated by the remote control unit will not be able to receive the 
IR light signal and respond to the command. In addition, IR remote control 
units have a limited operational range, which is sufficient for use within 
a room, but not sufficient for use between rooms. 
Currently, however, consumer electronic equipment is being placed inside of 
pieces of furniture, such as home entertainment units, behind solid doors. 
For example, a television, cable box, satellite receiver, etc., may be 
placed in a home entertainment unit in such a manner that, though the 
television receiver is visible to the viewer, the cable box, satellite 
receiver and VCR are placed behind solid doors. In addition, consumer 
electronic equipment is being distributed among different rooms in a home. 
For example, a satellite receiver might be located next to one television 
receiver in a family room, but may also coupled to a second television 
receiver in a bedroom. The IR light generated by remote control units 
cannot penetrate through solid doors or pass from room to room, so the 
hidden or remotely located equipment may not be controlled. 
To provide the capability of controlling consumer electronic equipment 
within cabinets or in different rooms of a home, IR repeaters have been 
developed. An IR repeater includes an IR receiver section located where it 
can receive the coded modulated IR signal generated by the remote control 
unit. For example, it may be located on the outside of an entertainment 
unit or in the room in which the remote control unit is being used. The IR 
receiver section is connected to an IR transmitter section located where 
the consumer electronic equipment which is to be controlled can receive 
its signal. For example, it is located inside of the entertainment unit or 
in the room in which the consumer electronic equipment is located. The IR 
transmitter section includes an IR light emitter which is placed so that 
the emitted IR light impinges on the IR receiver in the consumer 
electronic equipment to be controlled. More specifically, the IR light 
emitter is usually placed directly adjacent to the IR receiver in the 
consumer electronic equipment. The IR receiver section of the IR repeater 
detects the coded IR light signals produced by the remote control unit and 
transmits them to the IR transmitter section, usually via a wire. The IR 
transmitter section generates an IR light signal which is identical to the 
IR light signal received by the IR receiver section. The consumer 
electronic equipment receives this IR light signal from the IR transmitter 
section, and performs the desired function. 
Different manufacturers of consumer electronic equipment use different 
modulating frequencies for modulating the coded control signal onto the IR 
light signal. In order for IR repeaters to work with the respective 
manufacturers' modulation frequencies, IR repeaters use an IR detector in 
the IR receiver section which has a relatively wideband frequency response 
characteristic. That is, it will detect modulated IR light signals for 
which the modulating frequency can vary over a relatively wide range of 
frequencies. For example, IR repeaters can generally detect IR light 
signals which are modulated at any modulating frequency from about 20 
kilohertz (kHz) to 100 kHz. Any modulated IR signal in this frequency 
range may be detected by the IR receiver, and when detected, an IR signal 
mimicking the received signal is generated at the IR transmitter. 
Recently fluorescent lights having electronic ballast, termed compact 
fluorescent lights (CFLs), have been developed as a replacement for 
incandescent lights. CFLs use less energy than incandescent lights, and 
have become popular for that reason. However, CFLs produce IR light which 
has characteristics similar to those of the coded modulated IR light 
signals produced by remote control units. That is, the electronic ballast 
in a CFL causes the fluorescent tube to produce IR light signals which 
appear to be modulated by a modulating frequency in the range of 20 to 100 
kHz, and specifically by a frequency of about 56 kHz. In addition, the IR 
light produced by CFLs has an intensity far greater than that produced by 
remote control units. Thus, the IR light produced by a CFL completely 
overpowers the coded modulated IR light signal produced by a remote 
control unit. Because current IR repeaters mimic the IR signal received by 
its receiving section, any interference from nearby CFLs picked up by the 
IR repeater is also mimicked in the IR light signal produced by the IR 
repeater. It has been found that, in the presence of CFLs, IR repeaters 
have seriously degraded performance or even become completely inoperative. 
IR detectors have been developed which are resistant to interference caused 
by CFLs. These detectors can receive an IR light signal representing a 
coded modulated control signal from a remote control unit in the presence 
of interfering IR light from a CFL and, and in a known manner, cancel the 
interference from the CFL. The coded modulated IR light signal from the 
remote control unit is then demodulated, and such an IR detector produces 
an electrical signal representing the coded control signal. 
An IR repeater which can operate with remote control units from many 
manufacturers, and which can operate reliably in the presence of CFLs is 
desirable. 
SUMMARY OF THE INVENTION 
In accordance with principles of the present invention, an IR repeater, 
resistant to CFL interference, includes a receiver section for receiving 
an IR light signal representing a coded signal modulated by a modulating 
signal, and for detecting the coded signal. An oscillator generates a 
transmitter modulating signal, and a transmitter section generates an IR 
light signal representing the detected coded signal modulated by the 
transmitter modulating signal. 
If a CFL resistant IR detector is used in the receiver section, the effect 
of CFLs can be minimized, and the operation of the receiver portion will 
not be seriously degraded by CFLs. The receiver section is tuned to 
respond to a modulating signal center frequency about in the middle of the 
range of frequencies used by the respective manufacturers, and the 
frequency of the modulating signal produced by the oscillator is also 
about in the middle of that range of frequencies. Because the frequency of 
the modulating signal in the IR signal produced by the transmitter section 
of the IR repeater is about in the middle of the range of frequencies used 
by the respective manufacturers, it may be detected by the IR receivers in 
the consumer electronic equipment of any such manufacturer. In addition, 
the transmitter modulating signal is a clean signal produced by an 
oscillator in the repeater, not mimicked from the receiver section. Thus, 
the signal produced by an IR repeater according to the present invention 
will produce a clean modulated IR light signal, free of CFL interference.

DETAILED DESCRIPTION OF THE DRAWING 
In FIG. 1, a remote control unit 10 provides coded control signals 
modulated on an IR light signal to an IR light detector 25 of an IR 
receiver section 20 of an IR repeater. In the IR repeater of FIG. 1, the 
IR light detector 25 is illustrated as an IR phototransistor, although any 
IR light detecting device may be used. A control output terminal of the IR 
receiver section 20 is coupled to a control input terminal of a signal 
gate 30. A fixed frequency oscillator 40 has a signal output terminal 
coupled to a signal input terminal of the signal gate 30. A signal output 
terminal of the signal gate 30 is coupled to an input terminal of an IR 
transmitter section 50 of the IR repeater. The IR transmitter section 50 
is coupled to an IR light emitter 55 which produces an IR light signal 
corresponding to the electrical signal received at the input terminal of 
the IR transmitter section 50. In the IR repeater of FIG. 1, the IR light 
emitter is illustrated as an IR light emitting diode (LED), although any 
IR light emitting device may be used. This IR light emitter 55 is placed 
so that the IR light emitted impinges upon an IR light detector 65 of a 
piece of consumer electronic equipment 60. In FIG. 1, the IR light 
detector 65 is illustrated is an IR phototransistor, although any IR light 
detecting device may be used. In addition, the consumer electronic 
equipment 60 is illustrated as a television receiver, although the IR 
repeater of FIG. 1 will work with any consumer electronic equipment which 
can be remotely controlled by an IR remote control unit. 
In operation, the remote control unit 10 produces a coded modulated IR 
light signal. In the illustrated embodiment, the coded signal (described 
in more detail below) is a pulse code modulated (PCM) signal representing 
a command for the television receiver 60. This signal is detected by the 
IR phototransistor 25, which generates an electrical signal representing 
the coded modulated signal, and supplies that signal to the IR receiver 
section 20. The IR receiver section 20 demodulates the electrical signal 
from the IR light sensor 25, and produces a bistate signal representing 
the pulses making up the PCM signal. This signal has a first state 
representing the presence of modulated IR light at the IR phototransistor 
25, e.g. a logic `1` signal; and a second state representing the absence 
of modulated IR light at the IR phototransistor 25, e.g. logic `0` signal. 
This signal is supplied to the control input terminal of the signal gate 
30. 
The fixed frequency oscillator 40 produces a modulating signal having a 
frequency of around 47 kHz at its output terminal. This frequency is 
selected to be close to the middle of the range of frequencies (from 
around 32 kHz to around 56 kHz) used by respective manufacturers to 
modulate their PCM signals on the IR light signal from their remote 
control units. This modulating signal is supplied to the data input 
terminal of the signal gate 30. The signal gate 30 operates as a 
controllable switch. When the signal from the IR receiver section 20 is a 
logic `1` signal (representing the presence of modulated IR light at the 
IR phototransistor 25), the signal gate 30 is conditioned to pass the 
modulating signal at its signal input terminal to its output terminal. 
When the signal from the IR receiver section 20 is a logic `0` signal 
(representing the absence of modulated IR light at the IR phototransistor 
25), the signal gate 30 is conditioned to block the modulating signal at 
its input terminal. The output signal from signal gate 30 is an electrical 
signal representing the received coded signal modulated on a 47 kHz 
modulating signal. 
The signal from the signal gate 30 is supplied to the IR transmitting 
section 50. The IR transmitting section 50 conditions this signal to drive 
the IR LED 55 so that it produces an IR light signal corresponding to this 
modulated signal. The IR light signal produced by the IR LED 55, thus, is 
the pulse coded signal received by the IR phototransistor 25, but 
modulated on a 47 kHz modulating signal. This coded modulated IR light 
signal impinges on the IR phototransistor 65 in the television receiver 
65. The television receiver 60 responds in the normal manner to the 
received modulated coded IR light signal by executing the command 
represented by that coded signal. 
FIG. 2 is a waveform diagram useful in understanding the operation of the 
present invention. The waveforms illustrated in FIG. 2 represent the coded 
modulated signals as produced both by the remote control unit 10 (of FIG. 
1) and the IR LED 55 of the IR repeater. The differences between the 
signals produced by these respective sources will be described below. In 
FIG. 2, a series of code pulses axe illustrated. In FIG. 2a, the pulses 
axe arranged to form a pulse position coded signal. A series of clock 
pulses C1, C2, C3, . . . are produced with data pulses D1, D2, . . . 
interspersed between them. The time position of the data pulses D1, D2 . . 
. between the clock pulses C1, C2, C3, . . . determines whether a logical 
`1` or `0` is being transmitted during the interval between successive 
clock pulses C1, C2, C3, . . . . 
Referring to clock pulses C1 and C2 and data pulse D1, the data pulse D1 is 
closer in time to clock pulse C1 than to clock pulse C2. This represents a 
data bit having a logic `1` value. Referring now to clock pulses C2 and C3 
and data pulse D2, the data pulse D2 is closer in time to clock pulse C3 
than to clock pulse C2. This represents a data bit having a logic `0` 
value. Had the first data pulse been transmitted at the alternative time 
D1a, it would have represented a data bit having a logic `0` value, and 
had the second data pulse been transmitted at the alternative time D2a, it 
would have represented a data bit having a logic `1` value. A control 
signal comprises a predetermined number of data bits. 
FIG. 2b illustrates in more detail the composition of clock pulse C2 
illustrated in FIG. 2a. Each pulse illustrated in FIG. 2a has a 
predetermined pulse width, and is composed of cycles of IR light pulses 
occurring at the modulating frequency. In FIG. 2b, shaded areas represent 
the presence of IR light, and blank areas represent a lack of IR light. 
The envelope of the IR light pulses, repeating at the modulating 
frequency, defines the clock and data pulses illustrated in FIG. 2a. For 
the modulated coded pulses produced by the remote control unit 10 (of FIG. 
1), the modulating frequency is that used by the manufacturer of the 
remote control unit 10 (running from about 32 kHz to about 56 kHz.) For 
the modulated coded pulses produced by the IR LED 55 of the transmitting 
section 50 of the IR repeater, the modulating frequency is selected to be 
about 47 kHz. 
Referring again to FIG. 1, as described above, the IR light receiver 
section 20 is designed to detect and minimize the effects of spurious IR 
light emitted by CFLs. The IR light emitted by CFLs consists of successive 
groups of IR light pulses having a frequency between about 20 and 100 kHz. 
The light pulses have envelopes defined by the AC power supplied to the 
CFL. Within each half cycle of the AC power the CFL produces a group of IR 
light pulses. The envelopes of the groups have a duty cycle of around 50% 
and the groups occur at a frequency of about twice the AC power frequency. 
Specifically, it has been found that one type of CFL produces IR light 
pulses at around 56 kHz, with envelopes having a repetition frequency in 
the United States of 120 Hz and a duty cycle of 40%. The characteristics 
of these pulses are sufficiently different from those of the pulses 
illustrated in FIG. 2b that the IR receiver section 20 is able to detect 
IR light pulses having these characteristics and cancel or minimize their 
effect. 
As described above, the coded modulated IR light signal produced by the IR 
LED 55 of the IR transmitter section 50 may have a modulating frequency 
slightly different than that expected by the television receiver 60. 
However in an IR repeater application, this in not a problem. A remote 
control unit 10 operates from battery power and, thus, produces IR light 
at a relatively low power level. In addition, a remote control unit is 
generally operated at a relatively large distance from the television 
receiver, e.g. on the order of several feet away. The IR light receiver in 
the television receiver is sensitive enough to detect the IR light signals 
produced under these circumstances. But IR repeaters are generally coupled 
directly to the home AC power source and, thus, can produce IR light at a 
relatively high power level. Also, as described above, the IR LED 55 of 
the IR transmitter section 50 of the IR repeater is generally physically 
placed in close proximity to the IR phototransistor 65 of the television 
receiver. The relatively high power level of the IR light signal produced 
by the IR LED 55, and close proximity of the IR LED 55 and the IR 
phototransistor 65, more than overcomes the slight mistuning between the 
47 kHz modulating frequency produced by the IR repeater and the modulating 
signal frequency expected by the television receiver 60. 
As described above, the transmitter section of prior art IR repeaters 
produces an IR light signal which mimics that received by the receiver 
section. Thus, if the received IR light signal is corrupted with IR light 
from a CFL, the transmitted IR light signal will be similarly corrupted. 
The performance of such IR repeaters is greatly diminished in the presence 
of CFLs, and some are rendered completely inoperative. An IR repeater as 
illustrated in FIG. 1, however, uses a receiver section which is resistant 
to CFL interference. The output signal from such a receiver section 
(representing the demodulated coded signal) is used to modulate a clean 
oscillator signal from an oscillator within the IR repeater. This clean, 
newly generated, modulated signal controls the IR light emitter in the 
transmitter section. The IR light generated by the IR emitter in response 
to such a signal does not include any CFL interference, and its operation 
is not degraded in the presence of CFLs. 
FIG. 3 is a schematic diagram illustrating in more detail the IR repeater 
illustrated in FIG. 1. In FIG. 3, a source of operating power (not shown) 
produces a 5 volt power signal. A resistor R1 is coupled between the 
source of operating power and a collector electrode of an NPN transistor 
Q1. The signal electrodes of an IR detector 202 are coupled between an 
emitter electrode of the transistor Q1 and a source of a reference 
potential (ground). The IR detector 202 also receives operating power by 
being coupled to the source of operating power. The IR detector 202 is 
tuned to a modulating signal center frequency of 45 kHz and is a model 
GP1U78QG IR detector manufactured by Sharp Electronics Corporation. A 
resistor R2 is coupled between the source of operating power and a base 
electrode of the transistor Q1. A resistor R3 is coupled between the 
source of operating power and a collector electrode of an NPN transistor 
Q2. An emitter electrode of the transistor Q2 is coupled to ground. A 
resistor R4 is coupled between the source of operating power and a base 
electrode of the transistor Q2. A capacitor C1 is coupled between the base 
electrode of the transistor Q2 and the collector electrode of the 
transistor Q1, and a capacitor C2 is coupled between the base electrode of 
the transistor Q1 and the collector electrode of the transistor Q2. 
A resistor R6 is coupled between the source of operating power and a 
collector electrode of an NPN transistor Q3. A resistor R7 is coupled 
between an emitter electrode of the transistor Q3 and ground. A resistor 
R5 is coupled between the collector electrode of the transistor Q2 and a 
base electrode of the transistor Q3. The serial connection of a resistor 
R8 and an IR LED 55 is coupled between the source of operating power and a 
collector electrode of an NPN transistor Q4. An emitter electrode of the 
transistor Q4 is coupled to ground. The emitter electrode of the 
transistor Q3 is coupled to a base electrode of the transistor Q4. The IR 
LED 55 may be connected to the resistor R8 and the transistor Q4 via a 
long length of wire, e.g. meant to run from one room to another. The 
transistors Q1, Q2, Q3 and Q4 are all model MPS-A20 NPN transistors 
manufactured by Motorola Corporation. Table I contains preferred component 
values for the circuit illustrated in FIG. 3. 
In operation, the IR detector 202 detects the presence of IR light 
modulated at the predetermined modulating signal center frequency (e.g. 45 
kHz) while minimizing the effect of spurious IR light from CFLs, as 
described above. When modulated IR light is detected, the IR detector 202 
is conditioned to conduct current between its two signal electrodes, and 
when no modulated IR light is detected, the IR detector 202 is conditioned 
to become nonconductive. 
TABLE I 
______________________________________ 
Component Values 
______________________________________ 
R1,R3 1 k.OMEGA. 
R2,R4 100 k.OMEGA. 
R5 10 k.OMEGA. 
R6 1 k.OMEGA. 
R7 10 k.OMEGA. 
R8 100 .OMEGA. 
C1,C2 180 pf 
IR DET GP1U78QG 
Q1,Q2,Q3,Q4 MPS-A20 
______________________________________ 
When the IR detector 202 is nonconductive (indicating no modulated IR light 
is being detected), transistor Q1 is turned off, and both capacitors act 
as open circuits. The base electrode of the transistor Q2 is pulled high 
through resistor R4, and the transistor Q2 is turned on, pulling the 
voltage at its collector electrode to ground potential. The base electrode 
of transistor Q3 is pulled down through resistor R5, turning transistor Q3 
off. The base electrode of transistor Q4 is pulled down through resistor 
R7 turning transistor Q4 off, and preventing current from flowing through 
the IR LED 55. In short, when no modulated IR light is detected by IR 
detector 202, no IR light is emitted by IR LED 55. 
When the IR detector 202 is conductive (indicating that modulated IR light 
is being detected), the emitter electrode of the transistor Q1 is coupled 
to ground. The combination of the transistors Q1 and Q2, the resistors R1, 
R2, R3 and R4, the capacitors C1 and C2 and the IR detector 202 operates 
in a known manner as a multivibrator oscillator (40 in FIG. 1) adjusted to 
oscillate and generate a square wave at about 47 kHz. The signal at the 
collector electrode of the transistor Q2, thus, is a 47 kHz square wave 
signal produced during periods when modulated IR light is detected by the 
IR detector 202. The IR detector 202 operates as a switch turning the 
multivibrator on and off. The combination of the transistors Q3 and Q4, 
the resistors R5, R6, R7 and R8, and the IR LED 55 forms the transmitting 
section (50) and operates in a known manner as a two stage 
emitter-follower amplifier, responsive to the oscillator 40 output, to 
drive the IR LED 55 on and off at a frequency of 47 kHz during periods 
when modulated IR light is detected by the IR detector 202. Thus, the IR 
LED 55 generates a coded IR light signal modulated at a frequency of 47 
kHz. The IR detector 202 acts as the signal gate 30, controlling the 
transmission of the modulating signal from the oscillator 40 to the 
transmitting section 50. 
FIG. 4 is a schematic diagram illustrating an alternative embodiment for an 
IR detector 202 illustrated in FIG. 3. The IR detector 202 in the IR 
repeater illustrated in FIG. 3 is a single IR detector fabricated and 
tuned to have a modulating signal center frequency response of about 45 
kHz. 
In FIG. 4 the emitter electrode of the transistor Q1 is coupled to ground 
through the parallel connection of a first IR detector 204 and a second IR 
detector 206. The first IR detector 204 is tuned to a modulating signal 
center frequency of 38 kHz, and is a model TFMS1380 IR detector 
manufactured by TEMEC Telefunken Microelectronic GmbH. The second IR 
detector 206 is tuned to a modulating signal center frequency of 56 kHz, 
and is a model TFMS1560 IR detector, also manufactured by TEMEC. 
An IR repeater as described above provides reliable operation in the 
presence of CFLs and operates with a variety of manufacturers' equipment.