TIGER documentation

QDC mode

In QDC mode the charge is measured by sampling the peak voltage of the Energy branch shaper. The sampling time window duration can be programmed by the user through the channel configuration registers (max_integ_time and min_integ_time). These two parameters must be set with the same value and the sampling time duration is given by:

[math] t_{s} = 2 ⋅ T_{clk} + integ\_time ⋅ 4 ⋅ T_{clk} [/math]

where [math]T_{clk} = 6.25ns[/math] is the system clock period.

Settings

In order to operate the chip in S&H mode the following configuration registers must be set as follows:

• integ_en = 1
• qdc_mode = 1

Data decoding

Efine with wrap-around effect explained

The counter for the ADC performing the charge digitization has a wrap-around effect such that very high signals (just below the saturation point) have 1008 < Efine < 1024.

For these values the measurement is still linear, so in order to apply the usual conversion using the calibration line (Efine = const + slope * Qin) we need first to shift them by 1024. Therefore we can define a new variable Efine_new given by:

• Efine_new = Efine (for Efine < 1008)
• Efine_new = Efine - 1024 (for Efine > 1007)

In this way, the values of Efine between (1008, 1023) are shifted to the region (-16, -1) and thus correspond to the very high charge signals, with Efine_new = -16 being the new value of saturation. This is explained in the Figure on the right and the Table below.

Qin	Efine	Efine_new	Description
5	385	385	normal region
10	340	340	normal region
15	295	295	normal region
20	250	250	normal region
20	205	205	normal region
30	160	160	normal region
35	115	115	normal region
40	70	70	normal region
45	25	25	normal region
46	16	16	normal region
47	7	7	normal region
48	1022	-2	wrap-around region, still linear -> apply Efine_new
49	1013	-11	wrap-around region, still linear -> apply Efine_new
50	1008	-16	saturation
55	1008	-16	saturation
60	1008	-16	saturation

ToT mode

The Time-over-Threshold mode allows to measure the charge of the input signal from the pulse duration.

• It is typically performed on the T-branch shaper because of its better timing performance and thus depends on the threshold applied on this branch (VTH_T1)

• The ToT curve intrinsic non-linearity is due to the CR-RC shapers typical response

Settings

ToT calibration curves for different threshold settings

In order to operate the chip in ToT mode the following configuration registers must be set as follows:

• integ_en = 0
• qdc_mode = 0

Data decoding

• The ToT curve depends on the threshold level, thus the ToT measured on each channel can be converted into the correspondent input charge by applying the correct calibration curve (see Figure on the right)

• The ToT curves are fitted with the following function:

[math]ToT = E ⋅ e^{A ⋅ Q_{in} + B} + C + D ⋅ Q_{in}[/math]

• These curves must be inverted in order to retrieve back the input charge information

• Channel-by-channel TDC calibration files can be applied in order to improve the time binning of this measurement, otherwise limited to the clock period (6.25 ns)

Output words

TIGER output words

Event word

• identified by header 0b10
• 64 bits
• includes digitized information for each hit

Count word

• identified by header 0x01
• 64 bits
• includes information about internal counters

Framing word

• identified by header 0x00
• 64 bits
• sent with top priority after each 2^15 clock cycles (1 frame = 204.8 us)
• includes information about frame word used for time reference and SEU count detected for each frame

TIGER padframe

TIGER padframe