Electronic – Very high speed counter (around 1.5 GHz to 2 GHz)

counterdigital-logichigh frequencyRF

I am thinking of a device that can measure the distance of an object from a sensor using a radio transmitter and receiver pair.

I'm thinking of using a counter at the sensor side, with a fixed-frequency transmitter and receiver on the sensor.

There will also be a transmitter and receiver on the object whose distance with respect to the sensor I want to measure.

When the transmitter on the sensor transmits a pulse at the previously agreed radio frequency, the counter on the sensor will start counting.

When this pulse is detected by the receiver on the object, the transmitter on the object will transmit a pulse to be received by the receiver on the sensor at which moment the counter will stop and the distance will be measured according to the time lag.

The problem is that I can not find a counter and a clock source compatible with each other in the 1.5 GHz to 2 GHz range. Any suggestions as to what I can use?

The measurement error that is calculated is 33 cm/s at 1.4 GHz and 13 cm/s at 2.2 GHz. So basically, the faster the counter is, the less error.

Can anyone tell me what counter to use together with the clock source for the counter?

I looked at MC100EP016A counter IC but can not find a clock source for this IC.

I require a clock signal with the following characteristics:

  • Input high voltage = 2075 to 2420 mV
  • Input low voltage = 1355 to 1675 mV

Best Answer

Other answers have focused on why you might be approaching this the wrong way. Although I agree with those answers, what you're asking for does exist, so I'll go ahead and give you a straight answer. You'll likely find that this approach is more expensive than alternatives though.

What you want is a 2 GHz voltage-controlled oscillator (VCO) with 3.3-V LVPECL outputs. There are many vendors out there who make such parts.

If you don't find one with LVPECL output, since this is a clock signal, it's relatively easy to adjust the levels to something compatible with LVPECL by ac coupling and rebiasing. Any rf level between -3 and +2 dBm should be usable with a LVPECL input.

LVPECL parts like your 100EP016A can also accept single-ended inputs if you bias the complementary input to the midpoint between the normal logic levels (often there's even a pin called VBB that outputs this level for your convenience, but I didn't check if the 'EP016A has it).

You will then need to build a phase-locked loop to maintain the VCO output frequency accurately by comparing it with a low-drift reference oscillator, which could be anywhere from 10 to 100 MHz.

One part that provides both the VCO and PLL in one chip is Analog Devices' ADF4360-2

A couple more notes:

I noticed that the maximum guaranteed switching frequency of the MC100EP016A is only 1.2 GHz, so if you really want to do this at 2 GHz, you might want to look for another part. Maybe MC100E137, but then you'll need to have a 5 V supply and you'll also need to deal with the unequal timing of the different outputs for a ripple counter.

Finally, you'll need to deal with latching in all the bits of the count at exactly the same instant, so you don't capture some bits before a transition and some bits after. One solution to this is to use a gray-coded counter instead of a binary counter --- then only one bit changes for any transition, and the maximum error from latching delay variation is only a single count.

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