Hardware Space Components
PTGs. This stands for Polynomial Time Generator. This is a firmware construction that is used as a
timing signal to ramp voltages and signals.
Note
For most cases, the PTG2 should be selected.
There are two ways that a voltage ramp can be defined: Rate or Time. This parameter is selected under
Timing type (3). If the Timing type is set to Rate, the parameter in the Rate (4) data entry box will be
used to configure the sweep. In this case the rate is set at 1V/s, so entering 2 V into the Value will cause
the bias voltage to ramp from 1 V to 2 V at the rate of 1V/s. If the Timing Type was instead set to Time,
the Value in the Time (5) data entry box will be used to configure the sweep. In this case the time is set
to 1 ms, so entering 2 V into the Value will cause the bias to ramp from 1 V to 2 V in 1 ms.
The Status Bit and the Abort can be ignored for now. They are only used for more advanced
configurations. The Value Type is not used in the Hardware Space. This will be explained in the
Procedure Space section.
The next Panel to be described is the Offset DAC (B) Panel. The Value (6) of the Offset DAC is a
voltage that is typically used to null out any offsets in the Drive signal outputs. These voltages are
typically very small and set when the system is out of tunnel range, so it does not really matter if the
parameters are set to a hard or soft acceleration. When it does not matter if the value is a hard
acceleration, it is best to set it to hard acceleration.
The third Panel is the Oscillation Amplitude (C). As with the Offset DAC panel, the only parameter that
is important is the Value (7). This is the value of the AC modulation that will be added to the DC
component of the Bias Voltage. Set the Mode to Set Value. The other parameters can be ignored.
Note
The oscillation amplitude is specified in PEAK voltage. The PEAK voltage is the value from
zero volts to the positive peak of the AC waveform.
The next four dropdown boxes configure what signals are to be summed together and added to the Bias
voltage. All of these summing junctions are done in the digital domain, eliminating the noise that is
generated when analog summing junctions are used. For these four dropdown boxes, the choice is for
that particular signal to Sum into the Bias voltage, be Inverted and summed into the Bias voltage, or be
Disabled and not summed into the summing junction.
The R9 Control (8) dropdown box selects if the Value (1) in the Value Panel is added, inverted, or
disabled from the bias voltage. In most cases the setting would be Sum. If the Disabled setting is
selected, the Value in the Value Panel would not be added to the bias voltage.
The Oscillator Input (9) dropdown box selects if the Value (7) in the Oscillation Amplitude Panel is
added, inverted, or disabled from the bias voltage. In most cases the setting would be Sum. If the
Disabled setting is selected, the Value in the Oscillation Amplitude Panel would not be added to the
bias voltage. If the Oscillation Input is set to Sum, the oscillation can be set to zero by turning the Value
in the Oscillation Amplitude Panel to zero.
The Channel 1 ADC (10) dropdown box is used for testing purposes and is normally set to disable.
Enabling this input will output onto Ch 1 drive any voltage that is present on the Channel 1 ADC.
The Kelvin PI Input (11) dropdown box is used in Kelvin Force Microscopy measurements and allows the
output of the Kelvin Force feedback loop to be summed with the bias voltage. This parameter is set to
disable for STM experiments.
To Next Page
Loading...