Falco Systems WMA-100 User manual
USER MANUAL
●High voltage: 20x amplification up to +175V and -175V output voltage
●DC to 500kHz at (-3dB) large signal bandwidth and 100mA output current
●Very low noise: ~560µVrms, and even 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-100 high voltage
amplifier product. Please read it carefully
and pay attention to the recommendations
and instructions for safe use.
The WMA-100 amplifier:
getting started
The Falco Systems WMA-100 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 -175V to +175V, a
large 500kHz @ -3dB signal bandwidth, a
typical slew rate of 350V/µs, and a noise
level of ~560µVrms. 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-100 High Voltage Amplifier DC – 500kHz
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2
Recommendations:
- Never apply more than +15V (-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 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.
- Use the amplifier within its specified 15 -
30°C ambient operating temperature
range
- Unplug the WMA-100 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
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.
- This product is a Class I appliance which
requires a mains connection with
protective earth.
- Always position the WMA-100 amplifier
such that the on/off power switch is easily
accessible.
- The airflow to and from the WMA-100
amplifier should not be blocked or
impeded, both at the front and the back
side.
- The internal circuitry of the amplifier
operates at high voltage. Only qualified
personnel from Falco Systems should
service this amplifier.
- 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 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-
100 high voltage amplifier
Input
The input impedance of the WMA-100
high voltage amplifier is a 100kΩresistor
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 50Ωoutput function
generator) is connected to the input. The
noise will be slightly higher when the
amplifier input is left open.
The 100kΩresistor also adds to the output
offset voltage because the offset current of
the input amplifier generates a voltage
over this resistor.
A high-speed amplifier like the WMA-100
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 -8.75V to
+8.75V range. This will result (with an
amplification 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 amplifier. In this case, the amplifier
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 amplifier.
The WMA-100 amplifier 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
other high-speed negative feedback
amplifiers, often resulting in unwanted
output overshoot voltages, and, in extreme
cases, oscillations.
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3
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 (~560µVrms) is
lowest when a low-impedance source is
used, such as a pre-amplifier output or a
50Ωfunction generator output. An easy
way to assess the noise performance of
the amplifier without picking up
interference is to connect a 50Ωcoaxial
load resistor to the input (Fig. 2) and
monitoring noise voltage at the output with
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 for a detailed measured
curve).
Figure 2. If assessment of the amplifier
noise is necessary, connect e.g. a 50Ω
coaxial load resistor to the input to provide
a low-impedance input connection
Offset adjustment
The WMA-100 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:
~820µVrms instead of ~560µVrms.
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4
Figure 3. Offset circuitry ‘On-Off’ switch and offset control knob
The load
The output impedance of the WMA-100
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 piezos 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 50Ωload circuit is
possible by connecting a 50Ωresistor 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 50Ωgives 5V maximum
output voltage 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 their length should be
minimized. Otherwise 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-100 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)
- Cumulative output noise spectrum (Fig.
15)
- Rms output noise voltage versus
capacitive load (Fig. 16)
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5
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)
20
15
10
5
0
102103104105106107
0pF
100pF
1nF
10nF
100nF
1uF
10uF
Amplification factor
Frequency (Hz)
Amplification factor
20
15
10
5
0
102103104105106107
0pF
100pF
1nF
10nF
100nF
1uF
10uF
Time (ms)
Output voltage (V)
-150
-100
-50
0
50
100
150
2.01.51.00.50.0
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6
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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7
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 1.0µs
Figure 11b. 300Vpp step response 10-90%: down in 0.9µs
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
3.02.52.01.51.00.50.0
Time (µs)
Output voltage (V)
-150
-100
-50
0
50
100
150
3.02.52.01.51.00.50.0
!
8
Figure 11c. 0 to 150V step response 10-90%: up in 0.8µs
Figure 11d. 150 - 0V step response 10-90%: down in 0.8µs
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)
160
140
120
100
80
60
40
20
0
3.02.52.01.51.00.50.0
Time (µs)
Output voltage (V)
160
140
120
100
80
60
40
20
0
3.02.52.01.51.00.50.0
Time (µs)
Output voltage (V)
-150
-100
-50
0
50
100
150
20151050
!
9
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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10
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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