| 4,30 → 4,31 |
|---|
| |
| \sec Measured parameters |
| |
| Two prototypes of ADC modules were assembled and tested. The first prototype, labeled ADC1, has LTC2190 ADC chip populated with LT6600-5 front-end operational amplifier. It also has a 1kOhm resistors populated on inputs which give it an ability of an internal attenuation of the input signal. The value of this attenuation $A$ is calculated by the following formula \ref[ADC1-gain] |
| Two prototypes of ADC modules were assembled and tested. The first prototype, labeled ADC1, has LTC2190 ADC chip populated with LT6600-5 front-end operational amplifier. It also has a 1kOhm resistors populated on inputs which give it an ability of an internal attenuation of the input signal. The value of this attenuation $A$ is calculated by |
| |
| \label[ADC1-gain] |
| $$ |
| A = {806 \cdot R_1 \over R_1 + R_2} \eqmark |
| A = {806 R_1 \over R_1 + R_2} \eqmark\,, |
| $$ |
| |
| Where the letters stand for the following: |
| % |
| where |
| \begitems |
| * $A$ - Gain of an input amplifier. |
| * $R_1$ - Output impedance of signal source (usually 50 Ohm). |
| * $A$ - Gain of an input amplifier, |
| * $R_1$ - Output impedance of signal source (usually 50 $\Omega$), |
| * $R_2$ - Value of serial resistors at operational amplifier inputs. |
| \enditems |
| |
| We have $R_2 = 1000 \Omega$ and $R_1 = 50 \Omega$ which imply that $A = 0.815$. That value of A was further confirmed by the measurement. |
| In our measurement setup we have H1012 Ethernet transformer connected to inputs of ADC. We have used this transformer for signal symetrization from BNC connector at Agilent 33220A signal generator. Circuit diagram of the used transformer circuit is shown in picture \ref[balun-circuit] and circuit realization in photograph \ref[SMA2SATA-nest]. |
| We have $R_2 = 1000\, \Omega$ and $R_1 = 50\, \Omega$ which imply that $A = 0.815$. This value of A was further confirmed by the measurement. |
| In our measurement setup we have H1012 Ethernet transformer connected to inputs of ADC. We have used this transformer for signal symetrization from BNC connector at Agilent 33220A signal generator. Circuit diagram of the used transformer circuit is shown in Figure~\ref[balun-circuit] and circuit realization in Figure~\ref[SMA2SATA-nest]. |
| |
| \midinsert |
| \clabel[balun-circuit]{Balun transformer circuit} |
| \picw=10cm \cinspic ./img/SMA2SATA.pdf |
| \picw=7cm \cinspic ./img/SMA2SATA.pdf |
| \picw=8cm \cinspic ./img/SMA2SATA_nest1.JPG |
| \caption/f Simplified balun transformer circuit diagram. |
| \endinsert |
| |
| The signal generator Agilent 33220A which we used, does not have optimal parameters for this type of dynamic range measurement. Signal distortion and spurious levels are only -70 dBc according to Agilent datasheet \cite[33220A-generator]. We have managed to measure an ADC saturation voltage of 705.7 mV (generator output) with this setup, mostly due to an impedance mismatch and uncalibrated measurement setup, with 1V ADC range selected by sense pin. This is a relatively large error, but the main result of our measurement, seen as a FFT plot shown in image \ref[ADC1-FFT], confirms $>$80 dB dynamic range at ADC module input. |
| The signal generator Agilent 33220A which we used, does not have optimal parameters for this type of dynamic range measurement. Signal distortion and spurious levels are only -70 dBc according to Agilent datasheet \cite[33220A-generator]. We have managed to measure an ADC saturation voltage of 706 mV (generator output) with this setup. The main result of our measurement, seen as a FFT plot shown in Figure~\ref[ADC1-FFT], confirms $>$80 dB dynamic range at ADC module input. |
| |
| \midinsert |
| \clabel[ADC1-FFT]{ADC1 sine test FFT} |
| 36,19 → 37,15 |
|---|
| \endinsert |
| |
| |
| Similar test was performed at ADC2 module. For ADC2 we have to use formula with a different constant \ref[ADC1-gain]. The ADC2 module has LT6600-2.5 amplifiers populated on it with a gain equal to $A = 2.457$ and uses the same $R_2$ resistors. We measured saturation voltage of 380 mV (generator output) at channel 1 on this ADC. It is well within the parameter tolerances of the used setup. |
| Similar test was performed at ADC2 module. For ADC2 we have to use formula with a different constant |
| |
| \label[ADC2-gain] |
| $$ |
| A = {1580 \cdot R_1 \over R_1 + R_2} \eqmark |
| $$ |
| A = {1580 R_1 \over R_1 + R_2} \eqmark\,. |
| $$ |
| % |
| The ADC2 module has LT6600-2.5 amplifiers populated on it with a gain equal to $A = 2.457$ and uses the same $R_2$ resistors. We measured saturation voltage of 380 mV (generator output) at channel 1 on this ADC. It is well within the parameter tolerances of the used setup. Again, FFT plot shown in Figure~\ref[ADC2-FFT] confirms $>$ 80 dB dynamic range. |
| |
| Where the letters stand for the following: |
| \begitems |
| * $A$ - Gain of an input amplifier. |
| * $R_1$ - Output impedance of signal source (usually 50 Ohm). |
| * $R_2$ - Value of serial resistors at operational amplifier inputs. |
| \enditems |
| |
| \midinsert |
| \clabel[ADC2-FFT]{ADC2 sine test FFT} |
| 56,8 → 53,6 |
|---|
| \caption/f Sine signal sampled by ADC2 module with LTC2271 and LT6600-2.5 devices. |
| \endinsert |
| |
| Computed FFT spectra for measured signal are shown in the images \ref[ADC2-FFT] and \ref[ADC1-FFT]. Both images confirm that ADCdual01A modules have input dynamical range of at least 80 dB. |
| |
| \midinsert |
| \clabel[SMA2SATA-nest]{Used balun transformer} |
| \picw=15cm \cinspic ./img/SMA2SATA_nest1.JPG |