US 7,508,497 B2
Rangefinder with reduced noise receiver
John LaBelle, Long Beach, Calif. (US)
Assigned to Meade Instruments Corporation, Irvine, Calif. (US)
Filed on Nov. 23, 2004, as Appl. No. 10/995,687.
Claims priority of provisional application 60/525621, filed on Nov. 26, 2003.
Prior Publication US 2005/0110976 A1, May 26, 2005
Int. Cl. G01C 3/08 (2006.01)
U.S. Cl. 356—5.01  [356/5.07] 20 Claims
OG exemplary drawing
 
1. A rangefinder configured to determine a range to a target by measuring a flight time of a beam traveling between the rangefinder and the target, the rangefinder comprising:
a transmitter configured to emit the beam towards the target;
a receiver configured to detect a reflection of the beam from the target, the receiver comprising:
a photodiode configured to generate a current signal proportional to the received reflection;
a transimpedance amplifier configured to receive the current signal and to generate a voltage signal proportional thereto;
noise reduction circuitry configured to reduce noise present in the voltage signal by limiting the voltage signal relative to a first voltage level, the first voltage level selected according to a methodology of reducing said noise in said voltage signal;
a comparator configured to indicate when the noise-reduced voltage signal exceeds a second voltage level, the second voltage level selected above an expected noise in the noise-reduced voltage signal, thereby confirming that when said noise-reduced voltage signal exceeds said second voltage level, said received reflection comprises a desired reflection;
one or more filters configured to remove noise components from the voltage signal; and
an amplifier configured to amplify the voltage signal, wherein the amplifier is further configured to set a mean value of the voltage signal to the first voltage level; and
a processor configured to convert the flight time of the beam into a range measurement when the comparator indicates the noise-reduced voltage signal has exceeded the second voltage level.