Falco Systems WMA-100 User manual

Falco Systems WMA-100
High Voltage Amplier DC - 500kHz
USER
manual

Falco Systems WMA-100 • High Voltage Amplier DC - 500kHz
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Falco Systems WMA-100, High Voltage Amplier DC - 500kHz
• High voltage: 20x amplification up to +175V and -175V output voltage with respect
to ground
• DC to 500kHz at (-3dB) large signal bandwidth and 100mA output current
• Very low noise: ~350μVrms, and even lower when capacitive loads are driven
• No overshoot with capacitive loads: bandwidth changes automatically to
ensure stability
• Short-circuit protected output
• Adjustable DC offset
About this manual
This user manual is an integral part of the Falco Systems WMA-100 high voltage
amplier product. Please read it carefully and pay attention to the recommenda-
tions and instructions for safe use.
The WMA-100 high voltage amplier: getting started
The Falco Systems WMA-100 model is a high quality, cost-effective, high voltage,
linear laboratory amplier. Its wide bandwidth and large voltage range make it an
excellent choice for use with MEMS devices, EO-modulators, piezo positioning
systems, beam steering, ultrasonics, dielectric studies, and many other
applications. It is designed to be fully stable and free of spurious signals with
any capacitive load.
The amplication is 20x (xed). The amplier has a range of –175V to +175V, a
large signal bandwidth of 500kHz @ -3dB, a typical slew rate of 350V/μs, and
a noise level of ~350μVrms. The short-circuit protection with a fast current limit
of ±100mA make this amplier suitable for both normal daily laboratory use and
automated measurement systems.

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!
Recommendations:
• Never apply more than +15V (-15V) to the amplier input to prevent damage.
• A short voltage spike may appear at the output, when the amplier is turned on or off.
Pay attention not to damage sensitive circuitry or equipment already connected.
• The amplier cannot be damaged by a short-circuit condition or capacitive loading,
but two situations should be avoided:
- Connecting a charged capacitor to the input or output.
- Connecting a highly inductive load to the output (such as a coil).
• Do not connect anything to the output that can act as an antenna.
• This product should only be cleaned with a soft, slightly moist cloth. Unplug the
WMA-100 amplier from the mains power before cleaning.
Safety
• This product is able to produce over 175V at more than 100mA at its output, which is a
very high level (risk of electric shock). Safety measures should be taken accordingly.
This is indicated by the sign above the output connector of the amplier.
• This product is a Class I appliance which requires a mains connection with protective
earth.
• Always position the WMA-100 amplier such that the on/off power switch is easily
accessible.
• The airow to and from the WMA-100 amplier should not be blocked or impeded, both
at the front and the back side.
• The internal circuitry of the amplier operates at high voltage. Only qualied personnel
from Falco Systems should service this amplier.
• Only replace fuses with the correct type:
- 230V version of the WMA-100: 250V 250mA 5x20mm slow blow.
- 115V version of the WMA-100: 250V 500mA 5x20mm slow blow.
• The Falco Systems WMA-100 amplier is only suitable for indoor use in a class II
environment (domestic, light industrial).
• Non-sinusoidal mains power generators cannot be used to power this product.
Falco Systems WMA-100, High Voltage Amplier DC - 500kHz

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Detailed properties of the WMA-100 high voltage amplier
Input
The input impedance of the WMA-100 high voltage amplier is a 100kΩ resistor
to ground, in parallel with 68pF to prevent electrostatic discharge (ESD) input
damage. This resistor adds some noise to the output voltage unless a low-impe-
dance source (e.g. a 50Ω output function generator) is connected to the input.
The noise will be slightly higher when the amplier input is left open.
The 100kΩ resistor also adds to the output offset voltage because the offset
current of the input amplier generates a voltage over this resistor. This output
offset voltage is ~10mV if the input is left open. When the input is shorted or
connected to a low-impedance source, the offset is reduced to ~8mV.
A high-speed amplier like the WMA-100 model can never be made fully
insensitive to input overload conditions, as this would limit the performance of
the amplier signicantly. For normal operation, input voltages should remain
in the –8.75V to +8.75V range, resulting, with an amplication of 20x, in an
output voltage swing of –175V to +175V. Below -15V and above +15V, the input
protection circuitry will limit the voltage fed to the amplier, but the amplier may
be permanently damaged if the current of the source is not limited.
Output
The WMA-100 model has been designed to be fully stable with all capacitive
loads. It has been optimized for a perfect step-response, but it is also a very
good linear and sine-wave amplier.
The WMA-100 amplier has a clever feedback system, which ensures that
no signicant overshoot occurs at any capacitive load. The bandwidth of the
amplier is automatically reduced to ensure stability. Instability under capacitive
loading conditions is a common
problem of other high-speed negative feedback ampliers, often resulting in
unwanted output overshoot voltages, and, in extreme cases, oscillations.
Short-circuiting this amplier will not break down the amplier, due to the extre-
mely fast current limiting circuit that has been employed.
If output monitoring is required, it is recommended to connect a 10x oscil-
loscope probe to the output. A special BNC to probe tip connector is usually
supplied with the probe (Fig. 1). However, the user can choose a different way
of connecting the oscilloscope, as long as care is taken with the high output vol-
tage. Using non-coaxial cable can cause overshoot in the oscilloscope reading.

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Falco Systems WMA-100, High Voltage Amplier DC - 500kHz
Figure 1. A 10x probe connected for monitoring the output signal
Noise
The noise of the amplier (~350μVrms) is lowest when a low-impedance source
is used, such as a pre-amplier output or a 50Ω function generator output. An
easy way to assess the noise performance of the amplier without picking up
interference is to connect a 50Ω coaxial load resistor to the input (Fig. 2) and
monitoring noise voltage at the output with a sensitive amplier.
The output noise will be lower when the bandwidth of the amplier is reduced,
which happens when a signicant capacitive load is connected to the output
(see Fig. 16 for a detailed measured curve).
Figure 2. If assessment of the amplier noise is necessary, connect e.g. a 50Ω
coaxial load resistor to the input to provide a low-impedance input connection.

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Offset adjustment
The WMA-100 model provides an offset control knob to enable the amplier to
generate offset voltages over the full output range (Fig. 3). The offset control
can be switched to ‘Off’ with a small rocker switch on the front panel to obtain
the lowest noise and highest DC stability of the amplier. Turning the offset
control to ‘On’ enables the DC control knob.
The DC offset voltage reacts to adjustments of this knob in a second. With the
offset control turned to ‘On’, the noise performance of the amplier becomes
slightly higher: ~600μVrms instead of ~350μVrms.
Figure 3. Offset circuitry ‘On-Off’ switch and offset control knob

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The load
The output impedance of the WMA-100 model is 50Ω, to ensure stability with all
capacitive loads. The amplier is generally used for high-impedance ap-
plications where the load is capacitive. This is the case for MEMS devices,
EO-modulators and piezo’s alike. It should be noted that a coaxial cable itself
also presents a capacitive load of approximately 100pF/m. The cable that is
connected may limit the maximum usable current at high frequencies.
Matched loading with a 50Ω load circuit is possible by connecting a 50Ω resistor
in series with the output to ground, but is not recommended. The advantage is
that excessively long cables will not distort the waveforms. The disadvantage
is a highly reduced voltage range (100mA in 50Ω gives 5V maximum instead of
175V maximum).With sensitive and/or high-frequency measurements, coaxial
cables should be used for connecting both the input and the output, and its
length should be minimized. Otherwise the cables will cause overshoot due
to cable reections (an effect related to the nite speed of light), and current
limiting due to the cable capacitance. Although the amplier itself remains fully
stable, using less than 5 meter of output cable is recommended for
the WMA-100 amplier to obtain optimal results.
Transmitter mode
This amplier can generate a signicant amount of power at frequencies used
for radio transmission and reception. The amplier should not be used for
telecommunication as described in the R&TTE directive 95/5/EC. Also for this
reason always use coaxial cables.
Amplier characteristics
In the following pages, several amplier characteristics are illustrated:
• Frequency response as a function of capacitive load (Fig. 4, 5)
• Sine and triangle wave responses (Fig. 6, 7)
• Square wave response (Fig. 8, 9, 10)
• Step response (Fig. 11)
• Capacitive load dependency of square wave output (Fig. 12)
• Noise and offset with and without offset control engaged (Fig. 13, 14)
• Noise spectrum (Fig. 15)
• Rms output noise voltage versus capacitive load (Fig. 16)

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Figure 4. Frequency response at 300Vpp output voltage with different
capacitive loads
Figure 5. Frequency response at 1Vpp output voltage with different capacitive
loads

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Figure 6. Sine wave 300Vpp 1kHz
Figure 7. Triangle wave 300Vpp 1kHz

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Figure 8. Square wave 300Vpp 1kHz
Figure 9. Square wave 300Vpp 100kHz

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Figure 10. Square wave 1Vpp 100kHz (small signal response)
Figure 11a. 300Vpp step response 10-90%: up in 1.0μs

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Figure 11b. 300Vpp step response 10-90%: down in 0.9μs
Figure 11c. 0 to 150V step response 10-90%: up in 0.8μs

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Figure 11d. 150 - 0V step response 10-90%: down in 0.8μs
Figure 12a. 0pF load

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Figure 12b. 100pF load
Figure 12c. 1nF load

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Figure 12d. 10nF load
Figure 12e. 100nF load

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Figure 12f. 1μF load
Figure 12g. 10μF load
Figure 12. 300Vpp square wave response under different capacitive loading
conditions. The 100mA current limit limits the speed at which the capacitor can
be charged.The bandwidth adjustments of the amplier with different capacitive
loads preventing overshoot are clearly visible. Note the difference of the hori-
zontal timescale in the gures.