with the same signal, but with opposite
polarity. The outputs of the amplifiers are
connected in bridge mode. Fig. 1 shows
the concept of the bridge mode circuit.
Figure 1. Doubling the maximal output
voltage by using ‘bridge mode’
The WMA-IB-LN inverts the signal and
provides the signal for both amplifiers. The
outputs of the two amplifiers are
connected to the floating, ungrounded
load. The WMA-IB-LN phase inverter -
buffer amplifies 1x. If both amplifiers
amplify e.g. 20x, the total output voltage
across the load will be doubled in bridge
mode, i.e. 40x in this case.
Fig. 2 shows an actual setup with the ultra-
low noise phase inverter buffer connected
to two high voltage amplifiers to drive them
in bridge mode.
Figure 2. Connecting the high-speed
phase inverter buffer and two amplifiers for
bridge mode operation
When two amplifiers are driven in bridge
mode, the high voltage output signal with
twice the amplitude of the individual high
voltage amplifiers is available between the
inner pins of the two high voltage amplifier
BNC outputs and can be connected to the
load (Fig 3). Make sure that the load is not
grounded to the same ground as the
amplifiers, as this would short-circuit one
of the two high voltage amplifiers. This will
not damage the amplifier (if it is short-
circuit proof) but would reduce the output
voltage available to that of a single
amplifier only.
Figure 3. Connecting a load in bridge
mode to two WA-200 high voltage
amplifiers
Connecting the load
The ultra-low noise phase inverter - buffer
in combination with two Falco Systems
high voltage amplifiers is capable of both
relatively high bandwidth and ultra-low
noise performance. This performance can
only be obtained with correct shielding of
the cables connecting to the load and, if
possible, shielding of the load itself. Solid
BNC connectors and/or short, high quality
BNC cables are recommended.
Some loads, such as certain EO-
modulators, have a differential connector
available, or two individual connectors, to
drive them differentially (Fig. 4).
Figure 4. Shielded, differentially driven
load for bridge mode operation
The housing of the modulator is connected
to the shield of the cables this way,
resulting in good interference rejection.
-1x
Vin
Amp
Amp
Load
Load
Load
Cable 1
Cable 2
Shielding enclosure
