Falco Systems WMA-100A User manual

USER MANUAL
● High voltage: 20x amplification up to +170V and -170V output voltage
● DC to 500kHz -3dB large signal bandwidth and 100mA output current
● Very low noise: ~840µVrms in DC - 10MHz; lower with capacitive loads
● 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-100A high voltage
amplifier product. Please read it carefully
and pay attention to the recommendations
and instructions for safe use.
The WMA-100A amplifier:
getting started
The Falco Systems WMA-100A model is a
high quality, cost-effective, high voltage,
linear laboratory amplifier. 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 amplification is 20x (fixed). The
amplifier has a range of -170V to +170V, a
large 500kHz @ -3dB signal bandwidth, a
typical slew rate of 350V/μs, and a noise
level of ~840µVrms in DC – 10MHz. The
short-circuit protection with a fast current
limit of ±100mA makes this amplifier
suitable for both normal daily laboratory
use and automated measurement
systems.
Falco Systems WMA-100A High Voltage Amplifier DC – 500kHz

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Recommendations:
- Never apply a voltage higher than +15V
or lower than -15V to the amplifier input to
prevent damage.
- A short voltage spike may appear at the
output, when the amplifier is turned on or
off. Pay attention not to damage sensitive
circuitry or equipment already connected.
- The amplifier cannot be damaged by a
short-circuit condition or capacitive
loading, but avoid:
● 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.
- Use the amplifier within its specified 15 -
30°C ambient operating temperature
range.
- Unplug the WMA-100A amplifier from the
mains power before cleaning. Only clean
this product with a soft, slightly moist cloth.
Safety
- This product is able to produce over
170V 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.
- This product is a Class I appliance which
requires a mains connection with
protective earth.
- Always position the WMA-100A amplifier
such that the on/off power switch is easily
accessible.
- The airflow to and from the WMA-100A
amplifier should not be blocked or
impeded at the front, sides and rear panel.
- The internal circuitry of the amplifier
operates at high voltage. Only qualified
personnel from Falco Systems should
service this amplifier.
- Use the 230V and 115V versions of the
WMA-100A amplifiers with their intended
mains voltages only.
- Only replace fuses with the correct type:
● 230V version of the WMA-100A: 250V
250mA 5x20mm slow blow.
● 115V version of the WMA-100A: 250V
500mA 5x20mm slow blow.
- The Falco Systems WMA-100A amplifier
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.
Detailed properties of the
WMA-100A high voltage
amplifier
Input
The input impedance of the WMA-100A
high voltage amplifier 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-impedance
source (e.g. a 50Ω output function
generator) is connected to the input. The
noise will be slightly higher when the
amplifier input is left open.
The 100kΩ resistor adds to the output
offset voltage because the offset current of
the input amplifier generates a voltage
over this resistor. Driving the amplifier with
a low impedance source will prevent this.
A high-speed amplifier like the WMA-100A
model can never be made fully insensitive
to input overload conditions, as this would
limit the performance of the amplifier
significantly. For normal operation, input
voltages should remain in the -8.5V to
+8.5V range. This will result (with an
amplification of 20x) in an output voltage
swing of -170V to +170V.
Below -15V and above +15V, the input
protection circuitry will limit the voltage
being fed to the amplifier. In this case, the
amplifier may be permanently damaged if
the current of the source is not limited.
Output
The WMA-100A amplifier 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 amplifier.
The WMA-100A model has a clever
feedback system, which ensures that no
significant overshoot occurs at any
capacitive load. The bandwidth of the
amplifier is automatically reduced to
ensure stability. Instability under capacitive
loading conditions is a common problem of
high-speed negative feedback amplifiers,
often resulting in unwanted output
overshoot voltages, and, in extreme
cases, oscillations.

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Figure 1. A 10x probe connected for monitoring the output signal
Short-circuiting this amplifier will not break
down the amplifier, due to the extremely
fast current limiting circuit that has been
employed.
If output monitoring is required, it is
recommended to connect a 10x
oscilloscope 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 voltage.
Using a non-coaxial cable can cause
overshoot in the oscilloscope reading.
Noise
The noise of the amplifier (~840µVrms in
DC – 10MHz) is lowest when a low-
impedance source is used, such as a pre-
amplifier output or a 50W function
generator output. An easy way to assess
the noise performance of the amplifier,
without picking up interference, is to
connect a 50W coaxial load resistor to the
input (Fig. 2). The noise voltage at the
output can be measured using a sensitive
amplifier.
The output noise will be lower when the
bandwidth of the amplifier is reduced,
which happens when a significant
capacitive load is connected to the output
(see Fig. 16 on page 12 for a detailed
measured curve).
Figure 2. If assessment of the amplifier
noise is necessary, connect e.g. a 50W
coaxial load resistor to the input to provide
a low-impedance input connection
Offset adjustment
The WMA-100A model provides an offset
control knob to enable the amplifier 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 amplifier. 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 voltage level of
the amplifier becomes slightly higher:
~1150µVrms instead of ~840µVrms.

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Figure 3. Offset circuitry ‘On-Off’ switch and offset control knob
The load
The output impedance of the WMA-100A
model is 50Ω, to ensure stability with all
capacitive loads. The amplifier is generally
used for high-impedance applications
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. Excessively long cables
will not distort the waveforms, but the
disadvantage is a highly reduced voltage
range (100mA in 50Ω gives 5V maximum
output voltage instead of 170V maximum).
With sensitive and/or high-frequency
measurements, coaxial cables should be
used for connecting both the input and the
output, and their length should be
minimized. If not, the cables will cause
overshoot due to cable reflections (an
effect related to the finite speed of light),
and current limiting due to the cable
capacitance. Although the amplifier itself
remains fully stable, using less than 5
meter of output cable is recommended for
the WMA-100A amplifier to obtain optimal
results.
Transmitter mode
This amplifier can generate a significant
amount of power at frequencies used for
radio transmission and reception. The
amplifier should not be used for
telecommunication as described in the
R&TTE directive 95/5/EC. Always use
coaxial cables.
Amplifier characteristics
In the following pages, several amplifier
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 with and without offset control
engaged (Fig. 13, 14)
- Rms output noise voltage versus
capacitive load (Fig. 15)

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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
Figure 6. Sine wave 300Vpp 1kHz
Frequency (Hz)
Amplification factor
20
15
10
5
0
102103104105106107
0pF
100pF
1nF
10nF
100nF
1uF
10uF
20
15
10
5
0
102103104105106107
0pF
100pF
1nF
10nF
100nF
1uF
10uF
Frequency (Hz)
Amplification factor
Time (ms)
Output voltage (V)
-150
-100
-50
0
50
100
150
2.01.51.00.50.0

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Figure 7. Triangle wave 300Vpp 1kHz
Figure 8. Square wave 300Vpp 1kHz
Figure 9. Square wave 300Vpp 100kHz
Time (ms)
Output voltage (V)
-150
-100
-50
0
50
100
150
2.01.51.00.50.0
Time (ms)
Output voltage (V)
-150
-100
-50
0
50
100
150
2.01.51.00.50.0
Time (μs)
Output voltage (V)
-150
-100
-50
0
50
100
150
20151050

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Figure 10. Square wave 1Vpp 100kHz (small signal response)
In Figure 11 the unipolar and bipolar step response are shown
Figure 11a. 300Vpp step response 10-90%: up in 0.8μs
Figure 11b. 300Vpp step response 10-90%: down in 0.8μs
Time (μs)
Output voltage (V)
0.4
0.2
0.0
-0.2
-0.4
20151050
Time (μs)
Output voltage (V)
-150
-100
-50
0
50
100
150
43210
Time (μs)
Output voltage (V)
-150
-100
-50
0
50
100
150
43210

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Figure 11c. 0 to 150V step response 10-90%: up in 0.7μs
Figure 11d. 150 - 0V step response 10-90%: down in 0.7μs
In Figure 12 the 300Vpp square wave response under different capacitive loading conditions
is shown. The 100mA current limit limits the speed at which the capacitor can be charged.
The bandwidth adjustments of the amplifier with different capacitive loads preventing
overshoot are clearly visible. Note the difference of the horizontal timescale in the figures.
Figure 12a. 0pF load
Time (μs)
Output voltage (V)
140
120
100
80
60
40
20
0
43210
Time (μs)
Output voltage (V)
140
120
100
80
60
40
20
0
43210
Time (μs)
Output voltage (V)
-150
-100
-50
0
50
100
150
20151050

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Figure 12b. 100pF load
Figure 12c. 1nF load
Figure 12d. 10nF load
Time (μs)
Output voltage (V)
-150
-100
-50
0
50
100
150
20151050
Time (μs)
Output voltage (V)
-150
-100
-50
0
50
100
150
403020100
Time (μs)
Output voltage (V)
-150
-100
-50
0
50
100
150
200150100500

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Figure 12e. 100nF load
Figure 12f. 1μF load
Figure 12g. 10μF load
Time (ms)
Output voltage (V)
-150
-100
-50
0
50
100
150
2.01.51.00.50.0
Time (ms)
Output voltage (V)
-150
-100
-50
0
50
100
150
20151050
Time (ms)
Output voltage (V)
-150
-100
-50
0
50
100
150
200150100500

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11
Figure 13. Noise (~840µVrms measured with a true rms voltmeter in DC - 10MHz) with the
offset control switched to ‘Off’. The noise may appear to be higher than shown here if the
amplifier input is not connected to a low-impedance source.
Figure 14. Noise (~1150µVrms measured with a true rms voltmeter in DC - 10MHz) with the
offset control switched to ‘On’. In addition to the noise the short-term drift of the offset is
around 5mV.
Figure 15. Rms output noise voltage versus capacitive load measured in DC - 10MHz with
offset control switched ‘Off’
Time (ms)
Output voltage (mV)
-3
-2
-1
0
1
2
50403020100
Time (ms)
Output voltage (mV)
-4
-2
0
2
50403020100
Load capacitance (pF)
Rms output voltage noise (μV)
800
600
400
200
0
101102103104105106107

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Technical specifications
Amplification: 20x, fixed
Bandwidth: DC – 500kHz @ -3dB large signal bandwidth
Slew rate: 350V/μs typical
Output voltage: -170V to +170V
Current: 100mA typical with limiter
Noise and offset: 840µVrms output noise typical, 1mV DC offset typical
Input impedance: 100kΩ
Output impedance: 50Ω
Stability: stable with all capacitive and resistive loads, no overshoot > 5%
Power: 230V 50Hz AC, 50W or 115V 60 Hz AC, 50W
Mains fuse: 2x 0.25A 250V slow blow (230V version) or 2x 0.5A 250V slow blow (115V
version)
Safety: Class I - requires mains power connector with protective earth
Overvoltage: Category II
Operating temperature: 15 – 30°C
Storage temperature: 0 – 60°C
Relative humidity: 30 – 70% non-condensing
Maximum usage height: 2000m
Dimensions: 52 x 165 x 240mm
Weight: 2.5kg
Country of origin: The Netherlands
HS code: 8543 70 90
Specifications may be subject to change.

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Harmonized standards
This product complies with the following
standards:
Safety: EN61010-1
EMC: EN61326
FCC: 47 CFR 15
WEEE and RoHS
Do not dispose of the WMA-100A amplifier
as standard waste, but discard it at a
WEEE electronic waste collection point.
The amplifier has been built in compliance
with the RoHS directive.
Warranty
Falco Systems products are guaranteed
against malfunction due to defects in
materials or workmanship for a period of 1
year from the date on the invoice.
If a malfunction occurs during this period,
the product will be repaired or replaced
without charge. The product will be
returned to the customer free of charge.
The warranty does not apply to:
- Exterior finish or appearance.
- Malfunction of the product resulting from
use or operation in other ways than
specified in the user manual.
- Malfunctioning due to misuse or abuse of
the product.
- Malfunctioning occurring after changes or
repairs have been made by anyone other
than Falco Systems.
To obtain warranty service, inform Falco
Systems via [e-mail]
You will receive support and further
instructions.
Falco Systems will not be liable for any
consequential damages, including, without
limitation, devices or equipment connected
to the product, injury to persons or
property or loss of use. For more details
see the Falco Systems Standard Terms
and Conditions of Sale, which can also be
downloaded on www.falco-systems.com
User manual version
User manual version: 1.0
Date: October 26, 2021
Falco Systems
Falco Systems BV
Remisestraat 1
2225 TH Katwijk aan Zee
The Netherlands
Phone: [phone]
Email: [e-mail]
Website: www.falco-systems.com