The function of the Guard ring is to reduce the leakage current and make the PIN diode to work at higher potential ?
How does the guard ring perform this function?
Please some one explain elaborately how does the guard ring perform this function?
Kumar,
A guard ring is simply an equipotential conductor surrounding a signal-carrying conductor, this signal-carrying conductor usually being A) a pad or trace on a printed circuit board, B) a terminal of a device or C) a sensor or device. This "signal" could be generalized to mean any electrical charge or current of interest.
I think you are refering to my case "B" (or a combination of "B" and "A"). Will you please post an image, drawing or description of the specific application and guard ring? Include the recommended geometry or specifications of the guard ring.
A guard ring works by reducing the potential difference (voltage) to nearly zero, between the active (signal) conductor and the active conductor's surroundings. The guard ring is made to be "the surroundings". When the voltage is zero, no current can flow. Ohm's Law, V = I * R, or I = V/R. Although the resistance R may be large, for example across the plastic of a circuit board, the surest way to guarantee zero current is to reduce V to zero. This current that we are trying make zero is your "surface leakage current". Very simple, yes?
The technique, then, is to 1) build a guard ring completely surrounding your active conductor, and 2) bias the guard ring to a potential that is always equal to or close to the working potential of the conductor the guard ring is guarding. To create this guard ring bias voltage may be tricky, but I can post a circuit diagram of one way, if you like. But in general the guard ring bias voltage is generated using a low-impedance source, which can supply much more current than your leakage current would ever be, and still not 'sag' or get loaded down (i.e., the voltage will stay high, at the intended voltage). Then we have moved the source of leakage (stray, parasitic) current away from your sensitive, high-impedance signal circuit to a 'throw away', articifially created circuit, i.e., the guard ring and its 'driver' electronics. Thus your signal-of-interest stays 'clean', intact and true to its source.
As your signal circuit gets higher and higher in voltage above ground (common, return, LO), more and more leakage will occur. Maybe such leakage will be small (microamps, nanoamps or picoamps), but such small currents might be as large as your signal of interest. Moreover, such leakage currents are not well-behaved. They are usually stochasitic, intermittant, noisy and dependent upon many environmental variables (humidity, temperature and more). Guard rings are a brilliant way to eliminate the effects of such 'leakage', no matter what their cause or characteristics, which has been in use for probably 100 years.
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Kumar,
A guard ring is simply an equipotential conductor surrounding a signal-carrying conductor, this signal-carrying conductor usually being A) a pad or trace on a printed circuit board, B) a terminal of a device or C) a sensor or device. This "signal" could be generalized to mean any electrical charge or current of interest.
I think you are refering to my case "B" (or a combination of "B" and "A"). Will you please post an image, drawing or description of the specific application and guard ring? Include the recommended geometry or specifications of the guard ring.
A guard ring works by reducing the potential difference (voltage) to nearly zero, between the active (signal) conductor and the active conductor's surroundings. The guard ring is made to be "the surroundings". When the voltage is zero, no current can flow. Ohm's Law, V = I * R, or I = V/R. Although the resistance R may be large, for example across the plastic of a circuit board, the surest way to guarantee zero current is to reduce V to zero. This current that we are trying make zero is your "surface leakage current". Very simple, yes?
The technique, then, is to 1) build a guard ring completely surrounding your active conductor, and 2) bias the guard ring to a potential that is always equal to or close to the working potential of the conductor the guard ring is guarding. To create this guard ring bias voltage may be tricky, but I can post a circuit diagram of one way, if you like. But in general the guard ring bias voltage is generated using a low-impedance source, which can supply much more current than your leakage current would ever be, and still not 'sag' or get loaded down (i.e., the voltage will stay high, at the intended voltage). Then we have moved the source of leakage (stray, parasitic) current away from your sensitive, high-impedance signal circuit to a 'throw away', articifially created circuit, i.e., the guard ring and its 'driver' electronics. Thus your signal-of-interest stays 'clean', intact and true to its source.
As your signal circuit gets higher and higher in voltage above ground (common, return, LO), more and more leakage will occur. Maybe such leakage will be small (microamps, nanoamps or picoamps), but such small currents might be as large as your signal of interest. Moreover, such leakage currents are not well-behaved. They are usually stochasitic, intermittant, noisy and dependent upon many environmental variables (humidity, temperature and more). Guard rings are a brilliant way to eliminate the effects of such 'leakage', no matter what their cause or characteristics, which has been in use for probably 100 years.
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