Falco Systems WMA-IB-HS, Руководство пользователя

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Buffer mode
Although primarily intended for driving high
voltage amplifiers in bridge mode, the
WMA-IB-HS can also be used as a stand-
alone buffer to connect low power signal
sources to equipment with a 50
Ω input
impedance. Please note that computer-
controlled setups with DAQ (data
acquisition) cards often are not able to
drive a 50
Ω high voltage amplifier input
directly. This is caused by the very limited
current capability of the outputs of typical
DAQ cards, which is insufficient to drive a
50
Ω input.
An example is driving the input of a Falco
Systems WMA-300 high-speed high
voltage amplifier from a DAQ card. This
will result in a highly distorted and clipped
signal coming out of the DAQ card at
higher output voltages.
The solution is to use a WMA-IB-HS as
the buffer between the low current signal
source and the 50
Ω equipment (Fig. 7).
Figure 7. Using the WMA-IB-HS as a
buffer with a high input impedance to drive
a 50 Ω impedance
The input of the WMA-IB-HS is set to the
high impedance 100k
Ω setting not to load
the signal source unduly, and its ‘buffered
out’ will drive 50
Ω equipment without any
problems. If the signal coming from the
source is fast-changing, such as a square
wave or high frequency sine wave, then
mount the WMA-IB-HS very close to the
signal source. This is done to prevent
reflections in the non-50
Ω connection
between the signal source and the WMA-
IB-HS buffer input.
50
Ω : preserving signal
amplitude
The WMA-IB-HS is equipped with both a
50
Ω and a 100k Ω input. A typical 50 Ω
source such as a function or arbitrary
waveform generator has a 50
Ω output and
will form a 1:2 voltage divider with the 50 Ω
input resistance of the WMA-IB-HS. To
prevent the loss in signal amplitude due to
this voltage divider, the WMA-IB-HS
amplifies the signal at its input by a factor
2 when the input is switched to the 50
Ω
setting. The factor 2 ensures that the
signal at the output has the same
amplitude when driven from a 50
Ω source,
irrespective of whether the input is set to
50
Ω or 100k Ω .
If the signal source has a very low output
resistance and drives the 50
Ω input, the
voltage gain is 2x, because the 1:2 voltage
divider is absent. When the WMA-IB-HS
drives a high impedance load such as an
amplifier input, the voltage at the output
will be the same as the voltage at the
input. If the output drives a 50
Ω input, the
voltage divider consisting of the 50 Ω
output resistance of the WMA-IB-HS and
the 50
Ω input of the amplifier will divide
the signal available at the high voltage
amplifier input by a factor 2. This is just
what a 50
Ω signal source such as a
function generator would do. Fig. 8
illustrates the gain of the WMA-IB-HS for
different situations.
Figure 8a. 50 Ω generator, 100k Ω input,
high impedance load; Vout = Vin
Figure 8b. 50 Ω generator, 100k Ω input,
50 Ω load; Vout = Vin/2 (this also happens
without the WMA-IB-HS present, with only
the amplifier input loading the generator)
Figure 8c. 50 Ω generator, 50 Ω input, high
impedance load; Vout = Vin
Current
limited Vin
Buffer
100k Ω 50 Ω
Vin 1x
100k Ω 100k Ω
50 Ω
Vout = Vin
50 Ω
Generator WMA-IB-HS Amplifier input
Vin 1x
100k Ω
50 Ω
50 Ω
Vout = Vin/2
50 Ω
Generator WMA-IB-HS Amplifier input
Vin 2x
50 Ω 100k Ω
50 Ω
Vout = Vin
50 Ω
Generator WMA-IB-HS Amplifier input