Falco Systems WMA-100 Manuel utilisateur
USER MANUAL
●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
amplifier product. Please read it carefully
and pay attention to the recommendations
and instructions for safe use.
The WMA-100 high voltage
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 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 amplifier suitable for
both normal daily laboratory use and
automated measurement systems.
Falco Systems WMA
-
100
High Voltage Amplifier DC
–
500kH
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.
- This product should only be cleaned with
a soft, slightly moist cloth. Unplug the
WMA-100 amplifier 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
amplifier.
- 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. 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 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, resulting, 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,
but 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.
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 non-coaxial cable can cause
overshoot in the oscilloscope reading.
Figure 1. A 10x probe connected for monitoring the output signal
Noise
The noise of the amplifier (~350µVrms) 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 50Ωcoaxial 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 performance of
the amplifier becomes slightly higher:
~600µVrms instead of ~350µVrms.
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 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 50Ωload circuit is
possible by connecting a 50Ωresistor 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 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. Also for this
reason 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 and offset with and without offset
control engaged (Fig. 13, 14)
- Noise spectrum (Fig. 15)
- Rms output noise voltage versus
capacitive load (Fig. 16)
Frequency (Hz)
20
15
10
5
0
10
2
10
3
10
4
10
5
10
6
10
7
0pF
100pF
1nF
10nF
100nF
1uF
10uF
Amplification factor
Figure 4. Frequency response at 300Vpp output voltage with different capacitive loads
Frequency (Hz)
Amplification factor
20
15
10
5
0
10
2
10
3
10
4
10
5
10
6
10
7
0pF
100pF
1nF
10nF
100nF
1uF
10uF
Figure 5. Frequency response at 1Vpp output voltage with different capacitive loads
Time (ms)
Output voltage (V)
-150
-100
-50
0
50
100
150
2.01.51.00.50.0
Figure 6. Sine wave 300Vpp 1kHz
Time (ms)
Output voltage (V)
-150
-100
-50
0
50
100
150
2.01.51.00.50.0
Figure 7. Triangle wave 300Vpp 1kHz
Time (ms)
Output voltage (V)
-150
-100
-50
0
50
100
150
2.01.51.00.50.0
Figure 8. Square wave 300Vpp 1kHz
Time (µs)
Output voltage (V)
-150
-100
-50
0
50
100
150
20151050
Figure 9. Square wave 300Vpp 100kHz
Time (µs)
Output voltage (V)
-0.4
-0.2
0.0
0.2
0.4
20151050
Figure 10. Square wave 1Vpp 100kHz (small signal response)
Time (µs)
Output voltage (V)
-150
-100
-50
0
50
100
150
3.02.52.01.51.00.50.0
Figure 11a. 300Vpp step response 10-90%: up in 1.0µs
Time (µs)
Output voltage (V)
-150
-100
-50
0
50
100
150
3.02.52.01.51.00.50.0
Figure 11b. 300Vpp step response 10-90%: down in 0.9µs
Time (µs)
Output voltage (V)
160
140
120
100
80
60
40
20
0
3.02.52.01.51.00.50.0
Figure 11c. 0 to 150V step response 10-90%: up in 0.8µs
Time (µs)
Output voltage (V)
160
140
120
100
80
60
40
20
0
3.02.52.01.51.00.50.0
Figure 11d. 150 - 0V step response 10-90%: down in 0.8µs
Figure 11. Unipolar and bipolar step response
Time (µs)
Output voltage (V)
-150
-100
-50
0
50
100
150
20151050
Figure 12a. 0pF load
Time (µs)
Output voltage (V)
-150
-100
-50
0
50
100
150
20151050
Figure 12b. 100pF load
Time (µs)
Output voltage (V)
-150
-100
-50
0
50
100
150
403020100
Figure 12c. 1nF load
Time (µs)
Output voltage (V)
-150
-100
-50
0
50
100
150
200150100500
Figure 12d. 10nF load
Time (ms)
Output voltage (V)
-150
-100
-50
0
50
100
150
2.01.51.00.50.0
Figure 12e. 100nF load
Time (ms)
Output voltage (V)
-150
-100
-50
0
50
100
150
20151050
Figure 12f. 1µF load
Time (ms)
Output voltage (V)
-150
-100
-50
0
50
100
150
200150100500
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 amplifier with different capacitive loads preventing overshoot are clearly
visible. Note the difference of the horizontal timescale in the figures.
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