NetlistWriter

Description

Integrates micro-electronics simulation elements in the Allpix Squared simulation flow. Allows the user to generate netlists (input file used by an electrical simulator to simulate the behavior of the circuit) from a given netlist template. SPECTRE (Cadence environment) and SPICE syntax are allowed and can be selected using the target parameter. This module is mostly intended for analog front-end electrical simulation using the PixelCharge object data.

The netlist template needs to be formatted as described and illustrated (SPECTRE syntax) below:

• The netlist header.
• A sub-circuit describing the circuit of interest (analog front-end for example).
• If necessary, other instances (for example other voltage or current sources of the front-end).
• A current source, which will be used to replicate the electrical behavior of the collection electrode. A particular attention should be given to the polarity of the source.
• The sub-circuit written as an instance, connected to the source.
• The netlist footer and the simulator options.

--- netlist header ---

subckt front_end Pix_in Comp_vout Comp_vref SUB VDDA VSSA Vfbk

    description of the circuit 'front_end'

ends front_end

V1 (Comp_vref 0) vsource dc=Comp_vref type=dc
V2 (SUB 0) vsource dc=0 type=dc
V3 (Vfbk 0) vsource dc=Vfbk type=dc
V4 (VDDA 0) vsource dc=1.8 type=dc

Instance_source (0 Pix_in) isource type=pulse
Instance_front_end (Pix_in Comp_vout Comp_vref SUB VDDA VSSA Vfbk) front_end

--- netlist footer and simulator options ---

One way to get a netlist already formatted could be to extract it from the Cadence Virtuoso environment (“schematic” view).

A new netlist is written for each event, reusing the header, footer, and circuit description from the netlist template specified with the netlist_template parameter. For each fired pixel, a source / circuit instance pair is added to the template.

The new source written can be parameterized with the parameter source_type. Two different types of sources can be used: ISOURCE_PWL and ISOURCE_PULSE:

• ISOURCE_PWL allows writing all the temporal current waveform using a PWL (Piecewise Linear). This requires the use of the [PulseTransfer] module to get the current waveform. A delay can also be added using t_delay
• In order to lightweight the generated netlists, the ISOURCE_PULSE can be selected: it uses the total collected charge Q (instead of the current pulse). Charge and current are linked by $ Q = \int I(t)dt $. The current pulse is set with the parameters t_delay, t_rise, t_width and t_fall. The following equation is then used to determine the current: $ I=\frac{Q}{\frac{t_{rise}+t_{fall}}{2}+t_{width}} $

The generated netlist file name can be configured with a prefix taken from the file_name parameter, and contains the number of the event the netlist was generated for. The file extension is taken from the input netlist template file.

The pixel address is used to identify the fired pixels in the netlist, a linearization following

is used. Here, x and y are the respective pixel coordinates and $N_y$ is the number of pixels along y. This means that e.g. considering pixel (6,3) fired (7th column and 4th row) in a 10x10 matrix, the index 63 will be written in the netlist for this pixel..

The parameter waveform_to_save is used to write at the end of the generated netlist the waveform(s) to be saved (always using the index notation to identify the fired pixels). The electrical circuit simulation can be performed within the Allpix Squared event using the parameter simulator_command which is used to specify the command line to execute. Not setting it switches the feature off, setting a value will enable it. The generated netlist name to execute is appended at the end of the command, as illustrated below for SPECTRE syntax:

spectre -f nutascii <file_name_event1.scs>

If performed, the electrical simulation puts in stand-by the execution of the event. This electrical simulation is performed in the same terminal as the Allpix event, thus requiring the electrical simulator environment to be correctly set.

Parameters

• target: Syntax for the additional data to be written in the netlist, either SPECTRE or SPICE.
• netlist_template: Location of file containing the netlist template of the circuit in one of the supported formats.
• file_name : Generated netlist prefix name to which the event number is added as suffix. Defaults to output_netlist_event_.
• source_type: Type of current source to be used, ISOURCE_PWL and ISOURCE_PULSE.
• source_name: Name of the current source instance in the netlist.
• subckt_name: Name of the circuit the source is connected to.
• common_nets: Nets shared between the pixels.
• t_delay: delay from 0 before the current pulse starts, defaults to 0 ns
• t_rise: rise time of the current pulse, defaults to 1 ns, only works for the ISOURCE_PULSE
• t_width: width of the current pulse, defaults to 3 ns, only works for the ISOURCE_PULSE
• t_fall: fall time of the current pulse, defaults to 1 ns, only works for the ISOURCE_PULSE
• waveform_to_save: Name of the waveforms to save
• simulator_command: If specified, launches the electrical simulation. Command to be executed in the terminal, the generated netlist name is appended at the end of the command.

Usage

A possible configuration is using a ISOURCE_PWL and the SPICE syntax, requiring the collecting electrode capacitance:

[NetlistWriter]
target = SPICE
netlist_template = "front_end.asc"
source_type = ISOURCE_PWL
source_name = Instance_source
subckt_name = Instance_front_end
common_nets = Comp_vref, SUB, VDDA, VSSA, Vfbk
waveform_to_save = Pix_in, CSA_out, Comp_vout
simulator_command = "wine 'your\path\LTSpiceXVII\XVIIx64.exe' -run"

A current pulse ISOURCE_PULSE and the SPECTRE syntax is used is this example:

[NetlistWriter]
target = SPECTRE
netlist_template = "front_end.scs"
source_type = ISOURCE_PULSE
t_delay = 200ns
t_rise = 5ns
t_width = 20ns
t_fall = 5ns
source_name = Instance_source
subckt_name = Instance_front_end
common_nets = Comp_vref, SUB, VDDA, VSSA, Vfbk
waveform_to_save = Comp_vout
simulator_command = "spectre +aps -warn -info -log -debug -f nutascii"