Amplyfier for 20Mhz signal

[crutschow]

Do you know what an emitter-follower is? If not try Google.

 

[Icemetal]

Do you know what an emitter-follower is? If not try Google.

**broken link removed**

I set it up this way also, and the same problem but it works a bit better when I put a 1K resistor between the emitter and ground but the signal still distorted

 

[colin55]

I have tried both a transistor (1GHz) and a FET. Neither work. Use a SMD chip.

 

[Icemetal]

I have tried both a transistor (1GHz) and a FET. Neither work. Use a SMD chip.

I wish I could, but it seems like is acting up now the I was using a 74HCT04 hex inverter last night and the signal I guess was on the edge because is not working well today.

 

[Ubergeek63]

He doesn't need to mention his load. Even with a typical minimum circuit stray capacitance value, a common-emitter or common-source will not be able to drive it at 20MHz unless the collector/drain resistor is a low value.

i believe i just said that

 

[Roff]

What is the voltage swing of your input signal? What is the source of this signal?
Do you want a digital output, with 0V and 5V logic levels?

 

[Icemetal]

What is the voltage swing of your input signal? What is the source of this signal?
Do you want a digital output, with 0V and 5V logic levels?

yes is 0 to 5V


and I think i tried so many things I kinda give up I will pay $50 to anyone who can solve this problem

 

[Roff]

yes is 0 to 5v


and i think i tried so many things i kinda give up i will pay $50 to anyone who can solve this problem

Let's see if we have this straight. The source is a 20MHz sine wave swinging 1.8 to 2.5V, and you want 0 to 5V out. Is that correct?

EDIT: What is your signal source? Do you know the output impedance of that source?

 

[Icemetal]

this is my signal coming from the microcontroller is a 5V signal 20MHZ

**broken link removed**

this is what happen when I connect other chips to it,( I'm using SPI control and the clock signal is whats dropping)

**broken link removed**

 

[Roff]

How long is the wire (or trace) from the microcontroller to the "other chips"? How many other chips are connected, and what are they?
BTW, what was the "1.8V to 2.5V sine wave" you mentioned in post #5?

 

[Icemetal]

How long is the wire (or trace) from the microcontroller to the "other chips"? How many other chips are connected, and what are they?

The Microcontroller is a PIC32 and the slave are STP24DP05
the I'm trying to connect 8 STP24D05 about 6 inches apart from eachother, so the last chip is 4 feet away from the microcontroller.

 

[Roff]

The Microcontroller is a PIC32 and the slave are STP24DP05
the I'm trying to connect 8 STP24D05 about 6 inches apart from eachother, so the last chip is 4 feet away from the microcontroller.

You can't do that at 20MHz, due to transmission line effects. A transistor is not going to sove your problem. Are you trying to daisy chain them, or do you have a separate line from the µcontroller output to each STP24D05?
I couldn't find STP24D05 with Google. Can you provide a link to the datasheet?

 

[Icemetal]

You can't do that at 20MHz, due to transmission line effects. A transistor is not going to sove your problem. Are you trying to daisy chain them, or do you have a separate line from the µcontroller output to each STP24D05?
I couldn't find STP24D05 with Google. Can you provide a link to the datasheet?

this is the datasheet for the STP24D05
https://www.st.com/stonline/products/literature/ds/14714.pdf

 

[Roff]

What voltage are you using for Vdd on the STP24DP05? (You left out the P, which is why I couldn't find the datasheet).

You didn't answer all my previous questions.

 

[Icemetal]

What voltage are you using for Vdd on the STP24DP05? (You left out the P, which is why I couldn't find the datasheet).

You didn't answer all my previous questions.

I use 5V to drive the STP24DP05 , yes sorry I miss that part yes I'm daisy chain them there a single SPI bus line that runs 4 feet and each STP24DP05 feeds from that line.
What I will try to do is slow down the clock and see if it works that way, I will do it tomorrow I been playing with this since I got up this morning.

 

[Roff]

I use 5V to drive the STP24DP05 , yes sorry I miss that part yes I'm daisy chain them there a single SPI bus line that runs 4 feet and each STP24DP05 feeds from that line.
What I will try to do is slow down the clock and see if it works that way, I will do it tomorrow I been playing with this since I got up this morning.

You may have problems with any clock frequency. The long transmission line will have reflections. The problem is with the clock rise and fall times, not the frequency per se.
Can you post a drawing of your bus topology, or at least tell us the lengths of the stubs from the bus to each STP24DP05.
Do you have a ground plane on the side of the board opposite the bus?

 

[Ubergeek63]

I use 5V to drive the STP24DP05 , yes sorry I miss that part yes I'm daisy chain them there a single SPI bus line that runs 4 feet and each STP24DP05 feeds from that line.
What I will try to do is slow down the clock and see if it works that way, I will do it tomorrow I been playing with this since I got up this morning.

4 feet? and you were wondering why it was not working? you need special drivers and wires for RF at those distances

 

[Roff]

4 feet? and you were wondering why it was not working? you need special drivers and wires for RF at those distances

Some people learn about transmission lines in the school of hard knocks.

 

[Ubergeek63]

Some people learn about transmission lines in the school of hard knocks.

indeed ... all the while causing the rest of us to get hard knocks as our heads hit the walls!

 

[Icemetal]

indeed ... all the while causing the rest of us to get hard knocks as our heads hit the walls!

yeah I been hitting my head on the wall with this , sorry I should had mention it was 4 feet long, so what I did is change the clock speed from 20Mhz to 5Mhz and it works, the bad part is that I'm using a pic32 is a very powerful chip and is like driving a ferrari in traffic, I have to start doing more search on spi bus design.