Averaging circuit

An averaging circuit includes a number of sample/hold circuits which cyclically sample/hold an input signal, the outputs of the sample hold circuits being added and applied to a comparator. A further sample/hold circuit sample/holds an internal input signal at an increased rate and the output thereof is amplified by a factor equal to the number of cyclically operated sample/hold circuits before being applied as the other input to the comparator.

BACKGROUND OF THE INVENTION 
This invention relates to averaging circuits for processing signals which 
are periodically and intermittently input, and more particularly to an 
averaging circuit for an optical intensity signal received by an optical 
wave range finder. 
One example of the optical system of an optical wave range finder is as 
shown in FIG. 1. A modulated light beam is emitted from a light emitting 
diode 2 in the optical wave range finder 10. The modulated light beam is 
applied through a prism 9 and an objective lens 8 to a reflector 1 such as 
a corner cube placed at a measurement point. The modulated light beam 5 
reflected by the reflector 1 is received by a light receiving element 3, 
and the phase difference between the emitted and received modulated light 
beams is measured and converted into a distance. 
In this case, in order to eliminate a phase measurement error which is 
caused in the signal receiving circuit provided in the rear stage of the 
light receiving element, a method is employed in which a calibration light 
beam 4 (hereinafter referred to as "the internal light beam") is provided 
in the optical wave range finder 10, and the intensities of the internal 
light beam 4 and the modulated light beam 5 reflected from the reflector 1 
(hereinafter referred to as "the external light beam") are controlled by 
arranging a light quantity adjuster 6 such as a variable density filter or 
a diaphragm in one or two optical paths as shown in FIG. 1, so that the 
external light beam 5 and the internal light beam 4 as received are made 
equal in intensity. 
The internal light beam and the external light beam 5 are alternately 
produced by means of a light chopper 7 or the like. Therefore, the 
production sequence of the internal light beam 4 and the external light 
beam 5 is as shown in FIGS. 2a and 2b. 
FIG. 2a shows a pulsive external light beam, the light beam being provided 
at times indicated by "H". FIG. 2b shows the pulsive internal light beam, 
this light beam also being provided at the times indicated at "H" in FIG. 
2b. The external light beam 5 and the internal light beam 4 alternately 
provided in this fashion are received by the light receiving element 3. 
The intensities of the light beams 4 and 5 thus received are detected (the 
detection signals being referred to as "light quantity signals" 
hereinafter), and the intensities thus detected are made equal by means of 
the light quantity adjuster 6. This control is carried out manually or 
automatically. In order to control the light quantity adjuster 6 with 
respect to the production sequence of the external and internal light 
beams 5 and 4, in general, hold circuits for the light quantity signals of 
the external light beam 5 and the internal light beam 4 are disposed, so 
that, during reception of the external light beam 5, the light quantity 
signal of the external light beam 5 being received is compared with the 
light quantity signal of the internal light 4 which was held at the time 
of the internal light beam 4. Conversely, at the time the internal light 
beam is received, the internal light quantity signal being received is 
compared with the external light quantity signal previously held. A 
comparison output signal representative of the difference between the 
light quantity signals or their coincidence is used to control the light 
quantity adjuster 6. When coincidence is obtained, the light quantity 
adjuster 6 is stopped. In the case of manual control, the comparison 
output signal is displayed to inform the operator of the aforementioned 
difference or coincidence. In the case of automatic control, feedback 
control is effected according to the comparison output signal. In such a 
case, the internal light beam 4 is not affected by atmospheric conditions 
because it is inside the optical wave range finder, but the external light 
beam 5 is affected thereby (cf. FIG. 2d ). Especially in the case when 
there is schlieren, the intensity of the external light beam received is 
greatly varied, as a result of which the external light quantity signal 
varies greatly as indicated by the solid line in FIG. 2c. Accordingly, the 
comparison output signal is affected so greatly that the display or 
control is adversely affected. 
In order to prevent the comparison output signal from being affected as 
described, an averaging circuit such as an integration circuit or a time 
constant circuit is used, so the external light beam signal in one period 
is averaged as indicated by the dotted light in FIG. 2c, or the range of 
coincidence is increased, i.e., the control gain is decreased. However, 
the former method is not effective against variations over many periods, 
and the latter method is low in measurement accuracy, being poor in 
coincidence accuracy. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the invention is to provide a circuit in which 
the above-described difficulties have been eliminated and which is high in 
coincidence accuracy and averages variations over a number of periods.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 3 shows one example of a circuit for processing an internal light 
quantity signal and an external light quantity signal which includes one 
example of an averaging circuit according to the invention. FIG. 5 is a 
time chart showing the signals at essential sections of the circuit of 
FIG. 3. In FIGS. 3 and 5, like signals are designated by like reference 
characters (or names). In FIG. 3, reference numerals 11, 12, 13 and 14 
designate generally employed sample and hold circuits which are as shown 
in FIG. 4. Each sample and hold circuit has an analog signal input (a), a 
sample and hold control input (b), and a sample and hold output (c). 
Further in FIG. 4, reference numeral 23 designates a capacitor. 
A light quantity signal I is connected to the analog signal inputs (a) of 
the sample and hold circuits 11, 12 and 13, and is sampled and held 
according to the sample and hold control inputs (b) thereof. The outputs 
of the circuits 11 through 13 are applied to an adder 19 having a gain of 
one (1). The sample and hold control inputs V, VI and VII of the sample 
and hold circuits 11, 12 and 13 are the outputs of AND circuits 16, 17 and 
18, which receive the outputs of distribution control circuit 15, an 
external specifying pulse II and a sample signal IV. Therefore, the sample 
and hold circuits 11, 12 and 13 sample and hold the external light 
quantity signal I according to the sample signal IV when specified by the 
outputs of the distribution control circuit 15. The distribution control 
circuit 15 operates to output the count value of a ternary ring counter. 
The count value is of the ring type; 0, 1, 2, 0, 1, 2, and so on. The 
count clock input II is similar to that shown in FIG. 2a. As the 
distribution control circuit operates as described above, the outputs of 
the AND circuits 16, 17 and 18 (i.e., the sample and hold control inputs) 
are distributed, being subjected to 1/3 frequency division every period of 
the external specification pulse as is apparent from parts V, VI and VII 
of FIG. 5. One example of the outputs of the sample and hold circuit 11 
thus obtained is as shown in part IX of FIG. 5. 
On the other hand, the light quantity signal I is similarly applied to the 
analog signal input of the sample and hold circuit 14 which samples and 
holds the internal light quantity signal. The output of an AND circuit 22 
is connected to the sample and hold control input of the circuit 14. The 
AND circuit 22 receives the internal specifying signal III and the sample 
signal IV, to provide the output signal VIII. Therefore, the output VIII, 
being produced at every period of the internal specification pulse, 
samples and holds the internal light quantity signal. 
The outputs of the sample and hold circuits 11, 12 and 13 are applied to 
the adder 19 where they are subjected to addition. In this case, the 
output of the adder 19 is equivalent to three times the external light 
quantity signal. In order to allow the internal light quantity signal to 
coincide with the output of the adder 19, i.e., in order to increase the 
output of the sample and hold circuit 14 by the factor "three", the output 
of the sample and hold circuit 14 is applied to an amplifier 20. The 
output of the adder 19 and the output of the amplifier 20 are applied to a 
comparator 21, where they are subjected to comparison, i.e., the external 
light quantity signal and the internal light quantity signal are subjected 
to comparison. As a result, the comparator 21 outputs a comparison result 
representation of whether one signal is greater, smaller than, or equal to 
the other. 
The signals II, III and IV in FIG. 3 are outputted with suitable timing by 
means of a microprocessor or the like. The same effects as described above 
can be obtained by employing a microcomputer as the distribution control 
circuit 15. 
With the above-described arrangement, the variation of the external light 
quantity signal in one period thereof is reduced; that is, it is reduced 
to a third with respect to the output of the adder 19. Therefore, not only 
the variation in each period, but also the variation of the value held in 
each period is averaged. 
As is apparent from the above description, a plurality of circuits for 
sampling and holding the external light quantity signal are operated in 
such a manner that the circuits are switched every period, and the outputs 
of the plurality of sample and hold circuits are added to be subjected to 
comparison, whereby the effect of the variation in each period to the 
addition output is reduced, so that the variations of the signals over a 
number of periods are reduced and the display or control is made stable 
without increasing the range of coincidence. 
As was described above, in the case where the signals inputted periodically 
or intermittently are variable, the averaging circuit according to the 
invention, unlike the conventional averaging circuit, can average the 
variation of a signal over a number of periods. Thus, the averaging 
circuit of the invention can be effectively applicable to an optical wave 
range finder employing such signals.