Hi Everyone,
I'm having a bit of trouble identifying some anomalies in an analog signal. I am hoping somebody could point me in the right direction.
I currently have a high speed (50-100MHz) analog signal arriving from another board (via coax). On my board, this signal travels about 2" and then to a BNC connector where it leaves the board again. The purpose of my board is to measure the DC offset of the signal.
The Signal is composed of a transient non-sinusoidal signal (of roughly 50mV, ~50MHz) riding on a DC offset of roughly 200mV. The signal has an output impedance of 50 Ohms at it's origin, and is terminated as 50 Ohms off the board (on the BNC side).
I need a circuit in which i can sample the DC offset of this signal without interfering or distorting the signal. I've attempted to make a 50Ohm Impedance trace between co-ax and BNC connector on my board. This trace has a small stub coming off it going to a buffer voltage follower amp (LT1077) via a ~50kOhm resistor. The output of the buffer amp is then fed into other circuitry that requires lowish impedance, hence the buffer.
If i introduce this buffer op-amp into the circuit, i get an odd signal distortion, roughly 500ns after the signal first appears . If I remove it, it seems to attenuate significantly (though not entirely). If I bypass the board entirely, it disappears.
I've attached two images: One is the transient with the buffer amplifier in place via a 50k resistor, the other with the amplifier removed (via removal of the resistor). Both images are pictured averaged over 25 transients. Like previously mentioned, the problem disappears when the board is entirely bypassed.
Does the distortion pattern look familiar to anyone?
Could this be due to external noise being picked up by the board and made worse when the buffer amplifier is connected? The acquisition is triggered via laser, which can create a decent amount of electrical noise, this might also explain why it does not average out over 25 shots? The electronics are all within a grounded aluminum box, with a line filter on the power input.
Perhaps the answer is as simple as swapping the Op-Amp for something with a higher impedance input?
Any and all suggestions/criticisms welcome.
I'm sure I'm missing some info relevant to this question, so please ask if I've omitted anything.
Thanks
I'm having a bit of trouble identifying some anomalies in an analog signal. I am hoping somebody could point me in the right direction.
I currently have a high speed (50-100MHz) analog signal arriving from another board (via coax). On my board, this signal travels about 2" and then to a BNC connector where it leaves the board again. The purpose of my board is to measure the DC offset of the signal.
The Signal is composed of a transient non-sinusoidal signal (of roughly 50mV, ~50MHz) riding on a DC offset of roughly 200mV. The signal has an output impedance of 50 Ohms at it's origin, and is terminated as 50 Ohms off the board (on the BNC side).
I need a circuit in which i can sample the DC offset of this signal without interfering or distorting the signal. I've attempted to make a 50Ohm Impedance trace between co-ax and BNC connector on my board. This trace has a small stub coming off it going to a buffer voltage follower amp (LT1077) via a ~50kOhm resistor. The output of the buffer amp is then fed into other circuitry that requires lowish impedance, hence the buffer.
If i introduce this buffer op-amp into the circuit, i get an odd signal distortion, roughly 500ns after the signal first appears . If I remove it, it seems to attenuate significantly (though not entirely). If I bypass the board entirely, it disappears.
I've attached two images: One is the transient with the buffer amplifier in place via a 50k resistor, the other with the amplifier removed (via removal of the resistor). Both images are pictured averaged over 25 transients. Like previously mentioned, the problem disappears when the board is entirely bypassed.
Does the distortion pattern look familiar to anyone?
Could this be due to external noise being picked up by the board and made worse when the buffer amplifier is connected? The acquisition is triggered via laser, which can create a decent amount of electrical noise, this might also explain why it does not average out over 25 shots? The electronics are all within a grounded aluminum box, with a line filter on the power input.
Perhaps the answer is as simple as swapping the Op-Amp for something with a higher impedance input?
Any and all suggestions/criticisms welcome.
I'm sure I'm missing some info relevant to this question, so please ask if I've omitted anything.
Thanks