TDC-GPX datasheet(48/54 Pages) AMSCO

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TDC-GPX

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5.3 M-Mode Basics

Maximum resolution:

Standard deviation down to 10 ps,

Peak-peak down to 70 ps

2 stop-channels referring to 1 start channel

1 Hit per channel

0 ns to 40 µs measuring range

Quiet mode

LVPECL inputs

Max. 500 kHz continuous rate per channel

Max. 1 MHz continuous rate per chip

Start

Stop

Alutrigger

Figure 35: Measurement timings

Parameter

Time (Condition)

Description

tph

1.5 ns (min.)

Minimum pulse width

tpl

3.2 ns (min.)

Minimum pulse width

tss

0 ns (min)

40 µs (max.)

Start to Stop

tsa

400 ns (min)

Stop to ALU trigger

tva

1 µs (max.)

ALU trigger to data valid

M-Mode is activated by setting MSet = 31 (Reg3) and

Mon = 1 (Reg4).

The M-Mode for maximum resolution is basically an

extension of the R-Mode. The block diagram and the

input circuitry are the same as in R-Mode. Also the

furhter settings are the same as in R-Mode.

In this mode the TDC-GPX accepts only one Stop per

channel. It is necessary to select M-Mode in combina-

tion with quiet mode.

Input circuitry

In M-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 29.

Each input can be set to be sensitive to rising 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

triples, e.g Disable3, Disable4 and Disable5 to disable

DStop1.

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.

Start-Offset

For several reasons a programmable offset is added

to the stop time. One reason is to compensate for

different internal delays from the input buffers to the

TDC unit in the Start and Stop paths. It allows handling

Start-Stop intervals down to 0 and even less. The off-

set value ‘StartOff1’ is set in register 5 in multiples of

the I-Mode BIN and 18 bits wide. Internally the start

offset is added to the time measurement result and

has to be subtracted from the value read from the

TDC.

Adjusting the Start-Offset

The Start-Offset register of the TDC-GPX allows the

compensation for the offset due to the different inter-

nal delays. It allows to do measurements down to 0 ns

time intervals between Start and Stop. The correct

setting should be done by experiment.

Procedure for single start applications:

1. Set StartOff1 = 0

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