3
Figure 1. The 10x probe connected for monitoring the output signal
The load
The output impedance of the WMA-
01/01LF is 50kΩ. The amplifier is generally
used for high-impedance applications
where the load is mainly capacitive. This is
the case for MEMS devices, EO-
modulators and piezo actuators alike. It
should be noted that a coaxial cable also
presents
a
capacitive
load
of
approximately 100pF/m. The cables and
capacitance that are connected often limit
the maximum usable frequency due to the
first order RC filter formed by the output
resistance of the amplifier and the
connected capacitance.
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,
you can choose a different way of
connecting the oscilloscope, as long as
you mind the high output voltage. Pieces
of non-coaxial cable in the connection can
cause overshoot in the oscilloscope
reading.
The amplifier is capable of amplifying
above 9kHz, and should not be used for
telecommunication as described in the
R&TTE directive 95/5/EC. To prevent
unwanted radiation all cables should be
kept shorter than 30m.
Noise and offset
The WMA-01 is a low noise amplifier. The
output noise is typically below 3mV rms. If
this is not low enough, the dedicated
version WMA-01LF is available. It provides
less than 0.1mVrms noise: however, the
bandwidth is limited to DC – 50Hz (-3dB)
instead of DC – 20kHz (-3dB).
Power supply
Use a 24V DC power supply with a
continuous output current capability larger
than 200mA. If the power supply has an
adjustable current limit, it should be set at
200mA or higher too. Falco Systems offers
a suitable 24V power supply, for more
details please visit
www.falco-systems.com/products.html
Amplifier characteristics
In the following pages several amplifier
characteristics are shown:
- Frequency response (Fig. 2, 3)
- Square wave response (Fig. 4, 5, 6)
- Influence of a capacitive load on a
square wave output (Fig. 7)
- Triangle & sine response (Fig. 8, 9)
- Noise & offset (Fig. 10, 11)
