foreverloves said:i need a 1M resistor , but you know ,it takes too much silicon area, is there any methods that can realize large linear resistors?
switch capcitor may be a choice, but it may induce noises
if you have any good suggestions, tell me, thank you
foreverloves said:i need a 1M resistor , but you know ,it takes too much silicon area, is there any methods that can realize large linear resistors?
switch capcitor may be a choice, but it may induce noises
if you have any good suggestions, tell me, thank you
srivatsan said:I am just curious for the usage of 1M inside a chip? I am not too sure about the power dissipation capabilities.
Am I near-right with my assessment? I generally avoid high values as they are too tough to design... and may not work as intended.
Srivatsan
JPR said:Depending upon your application, you may be able to use a Tee network to approximate the large resistance.
Say, for example, you need to have an inverting amplifier with a gain of 100, and the input resistor is a 10kohm, and the maximum resistor size you can make is 50kohms. You would have the 50kohm resistor from your voltage to be amplified to the (-) input of the amplifier, and another 10kohm resistor from the (-) input to a common point for the tee network. You could have a 100ohm resistance from the common point to ground, and a 1.9kohm resistor from teh common point to the output of your amplifier.
If you put -1mV into the input, you would need +5mV at the other end of the 50kohm resistor. The 20:1 divider created by the 1.9k and 100ohm resistors would mean that the output of the amplifier would need to provide 20x, or +100mV to produce +5mV at the common point. This is the same gain you would obtain with a 1Megohm resistor in the feedback.
This is not EXACTLY right, since it negelects the current in the 50kohm resistor, but, if you need to be that exact, you could figure out the EXACT gain of the circuit, and adjust the 1.9kohm or 50kohm resistors to get the right gain. (I would guess that the solution given would be within a percent or so, and is probably close to what you would get with just resistor matching anyway...)
There are, of course, plenty of circumstances where the tee network will NOT yield the correct answer, and you will need either an off-chip resistor, or will have to accept the nonlinearities, etc. associated with a MOS resistance.
qutang said:can you use a current mirror?
JPR said:Again, this is somewhat specific, but perhaps useful:
A very long channel FET with Vgs-Vt just a bit larger than the voltage you plan on placing across the resistor will act as linear with fairly high value. The limitation of having Vgs-Vt larger than Vds will limit to cases where small Vds voltages apply (small voltage across the resistor). This type of resistor will also demonstrate voltage dependance (unless gate voltage and well track source voltage).
A bit less specific in application, but more specific to foundry:
There are some foundry specific high sheet rho resistors available, depending upon the foundry, but I think all of them involve extra processing steps, so inclusion on other foundrys may be limited.
Depending upon the application, you can turn a medium value resistor on for a small percent of time to make it appear (to a slow "observer") to be a large value resistor. For example, if you have a 100kohm resistor that is off for 990nSec, then on for 10nSec out of each 1uSec, it will appear as a 10Megohm resistor if used in a circuit with time constants of several uSec. Of course, to a fast "observer", this will look like exactly what it is, a 100kohm resistor that is switched on and off.
husseinadel said:hello
you can use high poly resistor ,,it will not consume very large area,,,
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