TDC-GPX datasheet(33/54 Pages) AMSCO

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TDC-GPX

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3.3 G-Mode Basics

In this mode the TDC-GPX offers:

2 Stop channels referring to 1 start channel

Each of 36 ps resolution

Rising and Falling edge for pulse width measure-

ment down to 1.5ns

Start-retrigger up to 5 MHz

4.7 ns pulse-pair resolution

0 to 65 µs measuring range

Minimum 32-fold multihit capability

Optional quiet mode

LVPECL inputs

Start

Stop

Alutrigger

Figure 25. Measurement timings

In this mode the TDC-GPX has two independent STOP

input channels, each one capable of measuring the

rising and falling edge at the same time. Each channel

can store minimum 32 hits.

For improvement of the measurement accuracy, two

channels are internally combined, which leads to a

resolution of typical 40 ps. The paired channels are

called combined channels. Each one of these combined

channels measures rising or falling edges of one sam-

pling channel. With this method it is possible to meas-

ure pulses with a pulse-width down to the minimum

pulse-width allowed by the differential inputs, which is

typ. 1.5 ns. Two adjacent rising or falling edges on a

sampling channel may have a delay of down to 5.5 ns

(typ.).

Each STOP input has an 8 Bit stop counter, sensitive

to the falling edge. The number of hits for each input

can be read from register 11, StopCounter0 and

StopCounter1.

Internally the Start is shifted by an offset (in multiples

of LSB). This allows measuring hits that arrive earlier

than the start signal and to measure down to 0.

Input circuitry

In G-Mode the TDC-GPX has differential low-voltage

PECL input buffers. The power for the differential in-

puts has to be switched on separately by setting regis-

ter 6, PowerOnECL = ‘1’.

The detailed input structure is shown in Figure 24.

Each input separately can be set to be sensitive to

rising and/or falling edge. This is done in register0,

RiseEn0..2 and FallEn0..2. A zero in both bits for one

channel at the same time disables the channel.

All inputs can be disabled by hardware, the stop inputs

separately for rising and falling edges (pin ‘StopDis1’

disables inputs DStop1, rising edge etc.).

They also can be disabled by software setting the ‘Dis-

able’ in register 2. The ‘Disable’ bits have to be set in

pairs, e.g Disable3 and Disable4 to disable Dstop,

falling edge.

StopDisStart & StartDisStop

By default the Start and Stop inputs of the TDC-GPX

are open immediately after a reset.

The consequence for the Stop channels is that even

hits coming before a Start pulse will be measured. The

bit StopDisStart in register 5 disables the Stop chan-

nels until there is a Start pulse. A consequence is that

there is a minimum delay of 7 ns after the Start before

hits are accepted on the Stop channels.

With single-start only the first Start pulse is used for

the measurement. In case more than one Start pulse

is expected this might cause an overflow of the Hit

FIFO of the Start channel. This will produce garbage

data. There we recommend setting the StartDisStart

bit in register 5. A ‘1’ disables the Start channel after

the first Start pulse.

External Start Retrigger

A further option is to retrigger the Start externally.

This option is activated by setting StartRetrig = 1 (Reg

5). The maximum retrigger frequency is limited to

typically 5 MHz. Higher rates will disturb the chip.

Parameter

Time (Condition)

Description

tph

1.5 ns (min.)

Positive pulse width

tpl

1.5 ns (min.)

Negative pulse width

tss

0 ns min

*5.2 ns min

64 µs (max)

Start to Stop

*with StopDisStart = 1

trr, tff

5.5 ns typ.

6.9 ns max.

equal edge to edge

# @ 87 ps resolution

trf,fr

1.5 ns (typ.)

Falling edge to rising

edge and v.v.

tva

107 ns (max.)

ALU start to data valid

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