Gated integrator preamplifier for infrared data networks

• US 5,790,295 A
• Filed: 08/28/1995
• Issued: 08/04/1998
• Est. Priority Date: 08/28/1995
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Apple Computer Incorporated (Apple Inc.)
• Inventors: Devon, Mark Daryl
• Primary Examiner(s): BACARES, RAFAEL D
• Application Number:
  US08/519,751
• Time in Patent Office: 1,072 Days
• Field of Search: 359/189, 359/190, 359/191, 359/192, 359/194, 359/195, 250/214 R, 250/214 A, 250/214 LA, 250/214 AL, 356/218, 356/223, 356/224, 356/226, 356/228, 330/59, 330/308
• US Class Current: 398/202
• CPC Class Codes: H04B 10/114 Indoor or close-range type systems

Abstract

A method and apparatus for receiving infrared signals are provided. The circuit includes preamplifier that includes an integrator that charges based on light detected by a photodiode. The circuit includes a warning circuit that generates a warning flag when the charge on the integrator exceeds a predetermined level. To prevent the integrator from saturation, digital logic resets the preamplifier by dumping the charge on the integrator in response to the warning signal. The digital logic is also configured to reset the integrator at predetermined intervals. When the incoming signal is encoded using pulse position modulation, the interval at which the integrator is reset is the length of a single time slot in the pulse position modulation frame. A sample and hold circuit is provided to hold a previous output of the preamplifier. The difference between the previous output of the preamplifier and the current output of the preamplifier is compared with a threshold voltage to detect pulses on the incoming signal.

Claims

1. A circuit for receiving infrared signals comprising:

a photodiode configured to generate a signal in response to detected light;

a preamplifier coupled to receive the signal from the photodiode, the preamplifier including an integrator that charges based on said signal from the photodiode;

a warning circuit coupled to the preamplifier, the warning circuit generating a warning signal when the charge on the integrator exceeds a predetermined threshold; and

a reset circuit coupled to the preamplifier and the warning circuit, the reset circuit being configured to reset the integrator in response to the warning signal.

2. The circuit of claim 1 wherein the reset circuit is further configured to reset the integrator at a predetermined frequency.

5. The circuit of claim 1 wherein said integrator stores a charge on a capacitor, said reset circuit resetting said integrator by causing a short between plates of said capacitor.

3. A circuit for receiving infrared signals comprising:

a photodiode configured to generate a signal in response to detected light;

a preamplifier coupled to receive the signal from the photodiode, the preamplifier including an integrator that charges based on said signal from the photodiode;

a warning circuit coupled to the preamplifier, the warning circuit generating a warning signal when the charge on the integrator exceeds a predetermined threshold;

a reset circuit coupled to the preamplifier and the warning circuit, the reset circuit being configured to reset the integrator in response to the warning signal;

a sample and hold circuit coupled to the preamplifier, the sample and hold circuit being configured to generate a first signal that reflects the current output of the preamplifier and a second signal that reflects a previous sampled output of the preamplifier; and

a post-amplifier gain stage coupled between the sample and hold circuit and a digital logic, the post-amplifier gain stage generating an amplified signal the reflects the difference between the first signal and the second signal.

4. A circuit for receiving infrared signals comprising:

a photodiode configured to generate a signal in response to detected light;

a preamplifier coupled to receive the signal from the photodiode, the preamplifier including an integrator that charges based on said signal from the photodiode;

a warning circuit coupled to the preamplifier, the warning circuit generating a warning signal when the charge on the integrator exceeds a predetermined threshold, wherein the warning circuit includes a comparator, wherein a first input of the comparator is coupled to the integrator and a second input of the comparator is coupled to a source of a constant DC voltage, said comparator generating said warning signal when the voltage at said first input exceeds the voltage at said second input; and

a reset circuit coupled to the preamplifier and the warning circuit, the reset circuit being configured to reset the integrator in response to the warning signal.

6. A circuit for receiving infrared signals comprising:

a photodiode configured to generate a signal in response to detected light;

a preamplifier coupled to receive the signal from the photodiode, the preamplifier including an integrator that charges based on said signal from the photodiode, said integrator storing a charge on a capacitor;

a warning circuit coupled to the preamplifier, the warning circuit generating a warning signal when the charge on the integrator exceeds a predetermined threshold;

a reset circuit coupled to the preamplifier and the warning circuit, the reset circuit being configured to reset the integrator in response to the warning signal, the reset circuit resetting said integrator by causing a short between plates of said capacitor; and

a transistor coupled to short said capacitor in response to a control signal, said reset circuit being configured to reset said integrator by generating said control signal to said transistor.

7. A method for preventing saturation in an infrared receiver, the method comprising the steps of:

generating a signal in response to detecting an infrared signal on a photodiode;

charging a capacitor in an integrator based on the signal from the photodiode;

dumping the charge on the capacitor when either a predetermined period of time has elapsed since a previous time that the charge was dumped or a charge on said capacitor exceeds a predetermined threshold.

8. A method for preventing saturation in an infrared receiver, the method comprising the steps of:

generating a signal in response to detecting an infrared signal on a photodiode;

charging a capacitor in an integrator based on the signal from the photodiode;

dumping the charge on the capacitor when either a predetermined period of time has elapsed since a previous time that the charge was dumped or a charge on said capacitor exceeds a predetermined threshold;

determining when charge on said capacitor exceeds the predetermined threshold by applying a voltage that reflects the charge on the capacitor to a first input of a comparator; and

applying a signal having a predetermined voltage level to a second input of the comparator.

9. A method for receiving a pulsed infrared signal in the presence of ambient light, comprising the steps of:

causing an integrator preamplifier to generate a first signal in response to detected light;

storing a first sample of said first signal taken during a first time slot;

comparing said first sample of said first signal with a second sample of said first signal to generate a difference signal, said second sample reflecting said first signal during a second time slot that is subsequent to said first time slot;

comparing said difference signal with a predetermined threshold voltage to generate a second signal; and

detecting pulses on said pulsed infrared signal based on said second signal.

10. The method of claim 9 further comprising the step of resetting the integrator preamplifier at a predetermined frequency.

11. The method of claim 10 further comprising the steps of:

detecting when the first signal exceeds a predetermined threshold; and

resetting the integrator preamplifier when the first signal exceeds the predetermined threshold.