Voltage Amplifier PD200 - Test Bench

1. Voltage Amplifier Requirements
2. PD200 Expected characteristics
3. Voltage Amplifier Model
4. Noise measurement
- 4.1. Setup
- 4.2. Results
5. Transfer Function measurement
- 5.1. Setup
- 5.2. Results
6. Conclusion

The goal of this test bench is to characterize the Voltage amplifier PD200 from PiezoDrive.

The documentation of the PD200 is accessible here.

1 Voltage Amplifier Requirements

Table 1: Requirements for the Voltage Amplifier
	Specification
Continuous Current	> 50 [mA]
Output Voltage Noise (1-200Hz)	< 2 [mV rms]
Voltage Input Range	+/- 10 [V]
Voltage Output Range	-20 [V] to 150 [V]
Small signal bandwidth (-3dB)	> 5 [kHz]

2 PD200 Expected characteristics

Table 2: Characteristics of the PD200
Characteristics	Manual	Specification
Input Voltage Range	+/- 10 [V]	+/- 10 [V]
Output Voltage Range	-50/150 [V]	-20/150 [V]
Gain	20 [V/V]
Maximum RMS current	0.9 [A]	> 50 [mA]
Maximum Pulse current	10 [A]
Slew Rate	150 [V/us]
Noise (10uF load)	0.7 [mV RMS]	< 2 [mV rms]
Small Signal Bandwidth (10uF load)	7.4 [kHz]	> 5 [kHz]
Large Signal Bandwidth (150V, 10uF)	300 [Hz]

For a load capacitance of \(10\,\mu F\), the expected \(-3\,dB\) bandwidth is \(6.4\,kHz\) (Figure 1) and the low frequency noise is \(650\,\mu V\,\text{rms}\) (Figure 2).

Figure 1: Expected small signal bandwidth

Figure 2: Expected Low frequency noise from 0.03Hz to 20Hz

3 Voltage Amplifier Model

The Amplifier is characterized by its dynamics \(G_a(s)\) from voltage inputs \(V_{in}\) to voltage output \(V_{out}\). Ideally, the gain from \(V_{in}\) to \(V_{out}\) is constant over a wide frequency band with very small phase drop.

It is also characterized by its output noise \(n\). This noise is described by its Power Spectral Density.

Figure 3: Model of the voltage amplifier

4 Noise measurement

4.1 Setup

Here are the documentation of the equipment used for this test bench:

Voltage Amplifier PD200
Load Capacitor EPCOS 10μF Multilayer Ceramic Capacitor
Low Noise Voltage Amplifier EG&G 5113
Speedgoat ADC IO313

The output noise of the voltage amplifier PD200 is foreseen to be around 1mV rms in a bandwidth from DC to 1MHz. If we suppose a white noise, this correspond to an amplitude spectral density:

\begin{equation} \phi_{n} \approx \frac{1\,mV}{\sqrt{1\,MHz}} = 1 \frac{\mu V}{\sqrt{Hz}} \end{equation}

The RMS noise begin very small compare to the ADC resolution, we must amplify the noise before digitizing the signal. The added noise of the instrumentation amplifier should be much smaller than the noise of the PD200. We use the amplifier EG&G 5113 that have a noise of \(\approx 4 nV/\sqrt{Hz}\) referred to its input which is much smaller than the noise induced by the PD200.

The gain of the low-noise amplifier can be increased until the full range of the ADC is used. This gain should be around 1000.

Figure 4: Schematic of the test bench to measure the Power Spectral Density of the Voltage amplifier noise \(n\)

4.2 Results

5 Transfer Function measurement

5.1 Setup

In order to measure the transfer function from the input voltage \(V_{in}\) to the output voltage \(V_{out}\), the test bench shown in Figure 5 is used.