• Mysterious wrong result for circuit with inductor?

    kodera2t • 07/05/2019 at 06:26 • 0 comments

    And let's measure 455 kHz IFT frequency response....

    We can see "shape" of response, but the issue is amplitude value. If I found just inductor can provide 40dB gain, I will get Nobel prize (or Edison medal?) As you see, the shape is correct, and it seems it has a resonant frequency of 439 kHz but its absolute value of amplitude is not reliable at all. This is not connection issue but may be impedance mismatch or,,,, transmission evaluation is made just by voltage, and multiplied voltage by IFT may producing miracle 40 dB.

  • Gain/Phase measurement of active circuit

    kodera2t • 07/05/2019 at 06:18 • 0 comments

    By using the embedded power supply, we can also measure active circuit without additional power supply.

    My adaptor has power supply pinout and let's connect V+, V- and GND to a... for example inverting amplifier.

    The output voltage can be set on Scopy. This time it is for op-amp power supply so let's make it "tracking" mode and set maximum voltage, 5V and push "Enable" to activate power supply.

    Now two BNC terminals can be connected to input and output of the circuit. Two GND clip are internally connected in the adaptor, but connect just to make it sure. (The frequency range is not so strict, but it is good habit to connect always.)

    The gain and phase response will be available after setting

    (1) Reference to Channel 2

    (2) signal level 500 mV

    (3) measurement frequency range from 50 Hz to 10MHz.

    As we can see in the result, this op-amp works perfectly under 100 KHz. Above around 200 kHz, both phase and amplitude are getting imperfect response.

  • First measurement of RC LPF

    kodera2t • 07/05/2019 at 05:58 • 0 comments

    Now let's start measurement. One important point before measurement is,

    We should NOT connect adaptor before calibration finishing!

    In the software named "scopy" by Analog Devices, initially it will recognize USB connection to the computer and click "connect" and the button will turn to "calibrating". Still we should not connect anything,

    and when the button turns to "disconnect", we can connect adaptor to ADALM2000 as below.

    The board as Ch1, Ch2, and green terminal for the embedded power supply. Now let' make a simple connection of RC circuit (In my case, 1k and 0.1 uF). Red clip are in/out of DUT and black ones are GND.

    Now let's go to Scopy. Indeed, all of available network analyzers are automatic for parameter setting, but NWA (network analyzer) of ADALM2000 is "full manual". All of parameter should be cared to get proper result.

    We have to set

    (1) Start, stop, step of frequency (as same as VNA).

    (2) Measurement signal level. If it is too small, S/N of the measurement will get worse, and if too large, some active DUT device will saturate and wrong response will be shown.

    (3) If you will use my adaptor, please set "REFERENCE" to "Channel 2" as above.

    If 1k/1uF LPF is measured with range from 100 Hz to 100 kHz, you will get the response as above by clicking "single".

    This circuit is not dynamic one and we don't need continuous measurement but if you prefer refreshing result, just click green "Run" button.

  • First of all, I made an adaptor for frequency response measurement.

    kodera2t • 07/05/2019 at 05:35 • 0 comments

    First of all, I made an adaptor with two BNCs and terminal adaptor for ADALM2000. The interface of ADALM2000 is just pin header and before I made this adaptor, every time I had to puzzle its connection.

    The schematic is as shown above. Ch 1 and 2 of the scope are connected to DUT (device under test). Indeed it is "counter intuitive" because one of two AWG (arbitral wave generator), AWG2 is connected to the output side of DUT. Initially I connected AWG1 and 2 for input and output, but AWG1 should be disconnected. The schematic above looks wrong, but it is the circuit measuring DUT in the direction of the image.

    This is the completed adaptor for frequency response measurement. If we prepare  AWG connection switch, it will be able to measure full two ports. Currently this is just for Ch1 to Ch2. Green terminal block is the power supply output inside ADALM2000. The power supply can generate max 50 mA, +/- 5V, which is suitable for quick operational amplifier circuit check.