Hi,
I continued working on the Current Injector.
The components in the attenuator for the monitor port were installed. This network gives a 30
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif)
resistance at the emitter of Q4 and output impedance of 50
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif)
The combined result is a monitor signal that is 1mV/mA
Testing Monitor Output![High Bandwidth Current Injector for Impedance measurements](https://www.eevblog.com/forum/index.php?action=dlattach;topic=238558.0;attach=974908;image)
The upper trace is the monitor output. The lower trace is the output current measured with a Tektronix P6022 probe.
ApplicationI am going to share one application of the current injector.
The current injector input is connected to the source of a network analyzer.
Channel R is connected to the monitor output of the current injector.
The current output is connected to a 1
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif)
resistor with a very short twisted cable.
Channel A of the VNA is connected across the resistor with a 50
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif)
cable.
1 Ohm Resistor![High Bandwidth Current Injector for Impedance measurements](https://www.eevblog.com/forum/index.php?action=dlattach;topic=238558.0;attach=974884;image)
A 1 Ohm resistor consisting of three 3
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif)
resistors connected in parallel is used as a standard.
The VNA configured to display channel A / Channel R
This is voltage / Current
![High Bandwidth Current Injector for Impedance measurements](https://www.eevblog.com/forum/index.php?action=dlattach;topic=238558.0;attach=974888;image)
This is the result. It is very flat but increases above about 50MHz.
This result is normalized on the VNA.
The VNA is now calibrated in dB
Measuring a capacitor![High Bandwidth Current Injector for Impedance measurements](https://www.eevblog.com/forum/index.php?action=dlattach;topic=238558.0;attach=974892;image)
A capacitor is connected in a similar way to the resistor.
Here is the graph:
![High Bandwidth Current Injector for Impedance measurements](https://www.eevblog.com/forum/index.php?action=dlattach;topic=238558.0;attach=974896;image)
The marker is indicating -9.21dB
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif)
at 100kHz
-9.21dB
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif)
= 0.346
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif)
C= 1/(2 x Pi x F x Xc)
C= 4.6uF ![High Bandwidth Current Injector for Impedance measurements](https://www.eevblog.com/forum/index.php?action=dlattach;topic=238558.0;attach=974900;image)
At the minimum the impedance is -46dB
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif)
-46dB
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif)
=
5m ![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif)
This is the ESR of the capacitor
![High Bandwidth Current Injector for Impedance measurements](https://www.eevblog.com/forum/index.php?action=dlattach;topic=238558.0;attach=974904;image)
With cursor at 20MHz the impedance is -17.3dB
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif)
-17.3dB
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif)
= 136m
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif)
L = Xl / 2 x Pi x F
L = 1.08nHThis illustrates how the current injector can be used to characterise a ceramic capacitor.
Regards,
Jay_Diddy_B