GAB/2
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10 GAB/2
10.1 Introduction
The AV4 GAB/2 is the successor of the BSMS/2 GAB/2 gradient amplifier. It supports all its
gradient functions, namely pulsed field gradients in NMR applications e.g. coherence
selection, gradient shimming, spoil. Additionally, the gradient control interface can be daisy-
chained, which enables triple axis gradient systems.
For the compensation of eddy current effects on the Z1, X1 or Y1 field in connection with
Gradient pulses, there has been a preemphasis built into the GAB/2. The preemphasis
current is based on three different exponential functions, each with a separate amplitude and
time constant. These three times six parameters can be configured by the CORBA interface
of the ELCB. In a multi gradient configuration, there are no cross terms available.
In spectrometers of the AV4 generation, the GTU uses the 48 bit LVDS link for real time
gradient control. Shaped gradient pulses can be transmitted with a time resolution of up to
one sample per microsecond.
For future applications it is possible to connect the GAB/2 with any other device issuing the
required real time gradient data. It is however necessary that the connected device fulfills the
LVDS interface specifications, which are given in detail later in this document.
The GAB/2 provides improved diagnostic functions and automatic offset calibration, which
are both implemented in the specific GAB/2 driver. This driver is part of the BSMS software
running on the ELCB.
In order to reduce distortions to a minimum, there is an improved, shielded connector for the
gradient cable to the probe head.
10.2 Technical Data
Parameter Min Typ. Max Unit Notes
Peak Current -10.0 +10.0 A 1)
Peak Voltage -33 33 Vs
Fall Time (90 - 10%) 10 µs 2)
Fall Time (residual current
smaller than 10 uA)
80 µs 2)
Amplitude Resolution for full
range -10 A to +10 A
16 20 3) bit
Residual current when there
is no Gradient active
-10.0 +10.0 µA
Preemphasis time constants 0.02 20 ms
Table10.1: Electrical Characteristics (typical values)
Notes concerning the electrical characteristics:
1. The peak current is provided during maximum 50 ms in a timeframe of 1 second.
2. Fall Time measurements with a load of 30 µH / 1 ohm.
3. Typical resolution of 20 bit with preemphasis.
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