Signal linear transformation problem

燕园技术宅

Signal linear transformation problem [Copy link]

 

Normally, the linear amplification of a small DC signal into a large signal can be achieved only through an amplifier circuit. The conversion of a DC signal with a higher voltage into a DC signal with a lower voltage can also be achieved through a simple circuit:

1. Resistor voltage divider + voltage follower.

2. The reverse amplifier circuit (-1~0 times) is used to amplify the current, and then amplify the current by -1 times. This circuit requires dual power supply, which is somewhat complicated.

3. I heard that there is an integrated chip that can directly realize linear conversion of DC signals.

4. Some people also say that voltage comparator can be realized.

5. Make a divider circuit (I have a general understanding of it, it seems to be very troublesome)/

If the signal needs to be collected by AD, and the source signal exceeds the input voltage range of ADC, the source signal needs to be reduced. The above two methods: method 1 may not guarantee accuracy, especially when the resistors need to be 1% or higher accuracy; method 2, dual power supply is a limitation in some cases. Methods 3 to 5 have not found actual cases.

It is mainly for conversion before ADC acquisition. Is there any other way to achieve this conversion? Or among the above 5 methods, can you give some suggestions or some typical corresponding cases?

燕园技术宅

Take the conversion of a DC signal of 0-5V to a DC signal of 0-3.3V as an example!

w522930954

It seems that the 5 circuits mentioned by the OP are all the first type. When your signal is <0, dual power supply is a must.

Regarding the first circuit, the problem of the original poster is the influence of the resistor accuracy. Any of the above circuits have the problem of resistor accuracy. The absolute accuracy of the resistor should be calculated by the original poster according to the actual accuracy requirements. If you do not want to increase the cost and use ordinary resistors, you must add a calibration link. Calibration equipment can help you ignore the accuracy of your resistors.

maychang

Method 1 may not guarantee accuracy, especially if the resistors are 1% or higher precision.

If you want accuracy, using high precision resistors is a must.

燕园技术宅

w522930954 posted on 2019-6-12 17:38 It seems that the 5 circuits mentioned by the OP are all the first circuits. When your signal is <0, dual power supply is a must. Regarding the first circuit, the OP must...

Is there a circuit that uses a voltage comparator?

燕园技术宅

maychang published on 2019-6-12 18:06 Method 1 may not guarantee accuracy, especially if the resistors have a precision of 1% or even higher. If you want accuracy, it is better to use high-precision resistors...

Some gas concentration sensors output 0-5V, but the ADC of the microcontroller is 3.3V. Usually, an additional ADC module can solve the problem. Because I encountered this problem, I want to know what different ways can be used to solve such a problem. I have tried two resistors (100% resistors) to divide the voltage proportionally, and then pass it through a voltage follower. The AD reading is relatively stable, but because there is no stable reference, I don’t know whether the error between the read number and the actual concentration is small enough. May I ask Teacher Maychang, is there a circuit that can achieve linear conversion using a voltage comparator? Someone mentioned it on the Internet before, but no clear circuit was given, and I didn’t find any related circuits.

w522930954

Resistor voltage divider is the simplest circuit, so why go to the extreme? If you can't make a comparator and you don't want to give up AD, you can try VF circuit, but the accuracy of resistors is still a problem you can't avoid.

maychang

Yanyuan Technology House published on 2019-6-13 08:55 Some gas concentration sensors output 0-5V, but the ADC of the microcontroller to be used is 3.3V. Usually, an additional ADC module can be used...

The voltage comparator is a device that works in a very strong nonlinear state. Even if it can be achieved, it is probably a laborious and thankless method to use the voltage comparator to achieve linear transformation.

maychang

Yanyuan Technology House published on 2019-6-13 08:55 Some gas concentration sensors output 0-5V, but the ADC of the microcontroller to be used is 3.3V. Usually, an additional ADC module can be used...

The additional ADC module is probably more expensive than a microcontroller and more expensive than two precision resistors plus a voltage follower.

燕园技术宅

maychang posted on 2019-6-13 09:29 Voltage comparator is a device that works in a very strong nonlinear state. If you want to use voltage comparator to achieve linear transformation, even if it can be achieved, it will probably be laborious...

That's it. Thank you, teacher.

燕园技术宅

w522930954 posted on 2019-6-13 09:27 Resistor voltage divider is already the simplest circuit, so why bother to go far away. If you can't make a comparator, and you can't bear to give up AD, you can try the vf circuit, but the resistor precision...

Thanks for your guidance

燕园技术宅

maychang posted on 2019-6-13 09:33 The additional ADC module is probably more expensive than the microcontroller and more expensive than two precision resistors plus a voltage follower.

Yes, considering the high cost, the ADC module is basically not included in the 5 methods mentioned above. Besides, except for the first two, the following methods are only heard to be feasible, but not actually implemented. I just want to accumulate some experience, so I raised this question in the forum. Thank you, Mr. Maychang.