There are several problems when ADC samples two sets of DAC output voltages, as shown in the figure. In addition, if the signal is about 1uA, does it need 20 bits?

QWE4562009

There are several problems when ADC samples two sets of DAC output voltages, as shown in the figure. In addition, if the signal is about 1uA, does it need 20 bits? [Copy link]

 

There are several problems when ADC samples two sets of DAC output voltages, as shown in the figure. In addition, if the signal is about 1uA, do we need a 20-bit ADC chip? Do we need to consider the frequency of the signal?

maychang

"Is the reference for this ADC sampling VDD3.3V?"

Many ADC chips have internal voltage references, so the chip voltage reference is not necessarily the power supply voltage. Without the chip model, it is difficult to say.

maychang

What are the functions of the three ??? pins of this ADC detection chip?

Not found??? Pin.

maychang

I have never seen the practice of using the pins marked AIN0 and AIN2 for ground connection and the pins marked GND for signal connection.

maychang

"If the signal is around 1uA, do I need a 20-bit ADC chip?"

The internal resistance of the signal source is very large. If the input impedance of your ADC chip is not large enough, just add a precision op amp to expand the current.

How many bits of ADC you use depends on how high resolution you require.

maychang

"Does the frequency of the signal need to be considered?"

Of course the signal frequency needs to be considered.

PowerAnts

Bandwidth and impedance are key to small signal processing

QWE4562009

maychang published on 2020-3-13 09:27 "If the signal is about 1uA, do you need a 20-bit ADC chip?" The internal resistance of the signal source is very large. If the input impedance of your ADC chip is not...

How many bits of ADC are needed to achieve a resolution of 10nA?

QWE4562009

PowerAnts published on 2020-3-13 09:36 The key to small signal processing is bandwidth and impedance

Are you talking about the bandwidth and output impedance of the signal?

QWE4562009

maychang posted on 2020-3-13 09:28 "Do we need to consider the frequency of the signal?" Of course we need to consider the frequency of the signal.

Is the sampling rate of this ADC adjustable by software or is it fixed on the chip?

maychang

QWE4562009 posted on 2020-3-14 17:35 How many bits of ADC do I need to have a resolution of 10nA?

If you need a 10nA resolution, you have to know what the full-scale current is so you can decide how many bits you need, right?

maychang

QWE4562009 posted on 2020-3-14 17:36 Is the sampling rate of this ADC adjustable by software or fixed by the chip?

Some ADC chips are software adjustable, some ADC chips are controlled by external components, and some ADC chips are controlled by clock frequency.

maychang

QWE4562009 posted on 2020-3-14 17:35 How many bits of ADC do I need to have a resolution of 10nA?

The first post says "if the signal is about 1uA", if the maximum current is 1uA and a 10nA resolution is required, then only an 8-bit ADC is needed. This is because an 8-bit binary number is 256, which means the resolution can reach 1/256, while 1uA/10nA is only 100.

PowerAnts

QWE4562009 posted on 2020-3-14 17:35 Are you talking about the bandwidth and output impedance of the signal?

You need to figure out the range you need, rather than just thinking about 20 bits when you see a small current of 1uA. Theoretically, if your minimum resolution is 1uA, then the highest range of 20 bits is 1A. Does your application really have such a large range?

If the purpose is to improve the resolution around 1uA, then the bandwidth and impedance of the sampling circuit determine the noise, which means that 20 bits is unnecessary.

PowerAnts

Costs should be spent where they are most useful, not put the cart before the horse

QWE4562009

maychang posted on 2020-3-14 17:39 If you need a 10nA resolution, you must know what the full-scale current is before you can say how many bits are needed, right?

The maximum current is 10uA

QWE4562009

PowerAnts posted on 2020-3-15 12:28 You need to figure out the range you need, instead of thinking about 20 bits when you see a small current of 1uA. In theory, if your minimum resolution is 1uA, then...

Minimum current 0.5uA Resolution 10nA Maximum current 10uA How do I choose the ADC? Is there any method?

QWE4562009

maychang posted on 2020-3-14 17:43 The first post said "If the signal is about 1uA", if the maximum current is 1uA, and 10nA resolution is required, then only an 8-bit ADC is needed. Because 8-bit binary...

1/256----What is the unit? 1uA/10nA----What does this mean?

maychang

QWE4562009 posted on 2020-3-16 11:37 The maximum current is 10uA

"The maximum current is 10uA"

10nA is one thousandth of 10uA. You need to resolve one thousandth of the full scale. 10 bits of binary is 1023, so your ADC will be sufficient if it has more than 10 bits.

maychang

QWE4562009 posted on 2020-3-16 11:41 1/256----What is the unit? 1uA/10nA----What does this mean

"1/256----what's the unit?"

It has no units; it is a dimensionless number that is the ratio of two currents.