TD250 V8 Manual
11
Rev 2, 31-09-2020
13
Noise
13.1
Noise Spectral Density
The noise density of the TD250 for a range of load capacitances is plotted in Figure 8. The noise
density is approximately 0.45
uV/√Hz
, with a first order low-pass response, where the bandwidth is
inversely proportional to load capacitance.
The total white noise of the TD250 is equivalent to the voltage noise of a 20 k
Ω
resistor at the input.
Since the equivalent input voltage noise of the TD250 is 18
nV/√Hz
, the noise of any driving source
should preferably be below 5 n
V/√Hz
, to avoid degrading performance.
The noise spectrum contains small periodic components at approximately 35 kHz and 70 kHz, which
arise from the power supply circuit. The amplitude of these narrowband components are significantly
smaller than the white noise, as observed in the time-domain plots in Section 13.3.
Due to the extremely low noise of the TD250, ground-loops between the TD250 and driving
instruments should be minimized. A ground loop effectively creates a large single turn coil, where any
stray magnetic fields will induce a small 50 Hz or 60 Hz voltage that is added to the signal. In cases
where large ground loops cannot be avoided, contact PiezoDrive for advice on minimizing
interference using isolation.
In critical piezoelectric positioning applications, other techniques are available to reduce positioning
noise levels. These applications are dealt with on a case by case basis depending on the application
requirements.
Figure 8. Output noise density for a range of load conditions in
𝐕𝐫𝐦𝐬/√𝐇𝐳
