# Why isn't there a buffer on an oscilloscope?

• Fips
In summary, an oscilloscope probe with a 1 megohm input resistance cannot be used to measure voltages lower than about 10 volts. Using a high impedance probe or buffer would increase the noise level in the circuit, and complicate the use of some options on the oscilloscope.
Fips
Today in my electronics class, we were introduced to the amp op concept. After going through some fundamentals, the teacher challanged us to find v0 of a simple circuit with a battery and two resistances of 1M ohm each(v0 is in between these resistances). Afterwards he asked us if this same value would be correctly read by an oscilloscope. The answer would be no because of the internal resistance of the oscilloscope (1M ohm) that would then be parallel with one of the resistances from the circuit.
One of my classmates then asked why wasn't there a buffer incorporated on the oscilloscope.

I went home and looked out what a buffer would do and realized that my classmate's question made a lot of sense. I tried to look up if buffer was high energy consuming or if it could short circuit both the oscilloscope and our circuit but with no success. Or maybe sometimes we want to module our wave through some options from the oscilloscope itself and using a buffer might complicate that. So my question is: why is this?

Thanks

Fips said:
Today in my electronics class, we were introduced to the amp op concept. After going through some fundamentals, the teacher challanged us to find v0 of a simple circuit with a battery and two resistances of 1M ohm each(v0 is in between these resistances). Afterwards he asked us if this same value would be correctly read by an oscilloscope. The answer would be no because of the internal resistance of the oscilloscope (1M ohm) that would then be parallel with one of the resistances from the circuit.
One of my classmates then asked why wasn't there a buffer incorporated on the oscilloscope.

I went home and looked out what a buffer would do and realized that my classmate's question made a lot of sense. I tried to look up if buffer was high energy consuming or if it could short circuit both the oscilloscope and our circuit but with no success. Or maybe sometimes we want to module our wave through some options from the oscilloscope itself and using a buffer might complicate that. So my question is: why is this?

Thanks
A typical 'scope probe has a 10:1 input impedance ratio, so you get a 10MOhm input impedance into the 1MOhm 'scope input.

There are reasons for not going to higher impedances, mainly noise pickup and reduced robustness. Some FET input probes have higher input impedance, but are very susceptible to damage by ESD. There are also some 100:1 'scope probes that I've used when I needed a higher input impedance, but they have reduced bandwidth, generally.

The standard 1 megohm input resistance of an oscilloscope permits series resistors to be used as attenuators for higher voltages. A standard 10:1 probe adds 9 megohm in series, EHT probes add 99 megohms or more to give 100:1 ranges.

Resistors over about 100k should not be used without protection from environmental contamination because unpredictable surface leakage currents may dominate the circuit. Most circuits have a much lower impedance than 1 megohm, hence it is rare that an oscilloscope needs a high impedance probe.

External high impedance probes and buffers or “electrometer amplifiers” are available. They need a power supply and so are usually only used on signals having voltages less than about 15 volts. They may have input currents equivalent to a 10G or 100G equivalent input resistance, but obviously cannot be used with series attenuator resistors or poorly insulated standard oscilloscope probes.

Fips, berkeman and DrClaude

## 1. Why is it important to have a buffer on an oscilloscope?

A buffer on an oscilloscope is important because it allows the oscilloscope to capture and store a larger amount of data before displaying it. This helps to prevent data loss and allows for a more accurate representation of the signal being measured.

## 2. Can I add a buffer to my oscilloscope?

In most cases, it is not possible to add a buffer to an oscilloscope. Buffers are typically built into the oscilloscope's circuitry and cannot be easily modified or added.

## 3. What are the disadvantages of not having a buffer on an oscilloscope?

Without a buffer, the oscilloscope may experience data loss or distortion, resulting in inaccurate measurements. The oscilloscope may also have a limited amount of memory, making it difficult to capture and display longer signals.

## 4. Do all oscilloscopes have buffers?

No, not all oscilloscopes have buffers. Some lower-end or older models may not have a buffer feature, while higher-end oscilloscopes typically have larger buffers to accommodate more data.

## 5. Can I use an external buffer with my oscilloscope?

It is possible to use an external buffer with an oscilloscope, but it may not be necessary. Modern oscilloscopes typically have built-in buffers that are sufficient for most applications. However, if you require a larger buffer, you can use an external buffer or memory module with your oscilloscope.

• Electrical Engineering
Replies
5
Views
3K
• Electrical Engineering
Replies
4
Views
2K
• Introductory Physics Homework Help
Replies
42
Views
2K
• Electrical Engineering
Replies
1
Views
2K
• Electrical Engineering
Replies
12
Views
2K
• Electrical Engineering
Replies
4
Views
2K
• Differential Equations
Replies
1
Views
1K
• Electrical Engineering
Replies
12
Views
2K
• Electrical Engineering
Replies
13
Views
2K
• Electrical Engineering
Replies
5
Views
820