Charge Pump - To Measure Distance

There are several projects where there is a need to measure distances of any object. Sensors are being used frequently for such type of applications but 3D optical measurement is still quite a difficult task for sensors.

The ability to tell the difference how far an object is from the sensor is very useful for imaging applications, and low cost components like sensors are mainly considered for this purpose. Now charge pump can play a significant role in getting all kind of information related to distance from the sensors.
There are two possible methods which can be used to take the information:

By processing a large amount of data quickly.

By modulated light source synchronized with the sensor.

Now, let’s take a brief idea of measuring a distance of any object with the help of modulated light source. Here the charge pump is a Photonic Charge Pump Mixer, a CMOS type, comprises two p-channel MOS transistors working in counter-phase clocking. A transmitter is also used to generate the light pulses which are focused on an imager. The light travel path causes the phase delay with respect to the source which at last is measured. The distance measured is proportional to the phase shift divided by the modulation frequency.

The bias condition makes the transistors to operate between inversion and accumulation conditions at each gate change. Now the minority charge carriers combines with the majority ones which are attracted from the substrate and convert into charge packets that flows to the source terminal. The important point of this device is that the transistor bias conditions depend on the light intensity and the conditions change when the light impinges on the part of the device. There is an integrator behind the charge pump on which the charge gets accumulated after the bias conditions get changed.

The two integrators are connected to two PMOS one at a left channel and the other at the right channel that work independently and the accumulated charge integrates at different time slots. This when synchronized with the modulated light source, the difference of the two outputs (VOR - VOL) is a measure of the light phase shifting and the distance of the backscattering object.


Author: Gary Jones (Component Engr.)
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