3D3608 Datasheet, PDF (2/7 Pages) Data Delay Devices, Inc. – 8-BIT & 12-BIT PROGRAMMABLE PULSE GENERATORS

3D3608 & 3D3612
APPLICATION NOTES
GENERAL INFORMATION
Figure 1 illustrates the main functional blocks of
the 3D3608 & 3D3612. Since these devices are
CMOS designs, all unused input pins must be
returned to well-defined logic levels, VDD or
Ground.
The pulse generator architecture is comprised of
a number of delay cells (for fine control) and an
oscillator & counter (for coarse control). Each
device is individually trimmed for maximum
accuracy and linearity throughout the address
range. The change in pulse width from one
address setting to the next is called the
increment, or LSB. It is nominally equal to the
device dash number. The minimum pulse width,
achieved by setting the address to zero, is called
the inherent pulse width.
For best performance, it is essential that the
power supply pin be adequately bypassed and
filtered. In addition, the power bus should be of
as low an impedance construction as possible.
Power planes are preferred. Also, signal traces
should be kept as short as possible.
PULSE WIDTH ACCURACY
There are a number of ways of characterizing the
pulse width accuracy of a programmable pulse
generator. The first is the differential nonlinearity
(DNL), also referred to as the increment error. It
is defined as the deviation of the increment at a
given address from its nominal value. For most
dash numbers, the DNL is within 0.5 LSB at
every address (see Table 1: Pulse Width Step).
The integrated nonlinearity (INL) is determined
by first constructing the least-squares best fit
straight line through the pulse-width-versus-
address data. The INL is then the deviation of a
given width from this line. For all dash numbers,
the INL is within 1.0 LSB at every address.
The relative error is defined as follows:
e_rel = (t_PW – t_inh) – addr * t_inc
where addr is the address, t_PW is the measured
width at this address, t_inh is the measured
inherent width, and t_inc is the nominal increment.
It is very similar to the INL, but simpler to
calculate. For most dash numbers, the relative
error is less than 1.0 LSB at every address (see
Table 1).
The absolute error is defined as follows:
e_abs = t_PW – (t_inh + addr * t_inc)
where t_inh is the nominal inherent delay. The
absolute error is limited to 1.5 LSB or 3.0 ns,
whichever is greater, at every address.
The inherent pulse width error is the deviation of
the inherent width from its nominal value. It is
limited to 2.0 ns from the nominal inherent pulse
width of 10 ns.
PULSE WIDTH STABILITY
The characteristics of CMOS integrated circuits
are strongly dependent on power supply and
temperature. The 3D3608 & 3D3612 utilize novel
compensation circuitry to minimize the
performance variations induced by fluctuations in
power supply and/or temperature.
With regard to stability, the output pulse width of
the 3D3608 & 3D3612 at a given address, addr,
can be split into two components: the inherent
pulse width (t_inh) and the relative pulse width (t_PW
- t_inh). These components exhibit very different
stability coefficients, both of which must be
considered in very critical applications.
The thermal coefficient of the relative pulse width
is limited to ±250 PPM/C (except for the -0.25),
which is equivalent to a variation, over the -40C
to 85C operating range, of ±1.5% (±9% for the
dash 0.25) from the room-temperature pulse
width. This holds for all dash numbers. The
thermal coefficient of the inherent pulse width is
nominally +20ps/C for dash numbers less than 5,
and +30ps/C for all other dash numbers.
The power supply sensitivity of the relative pulse
width is ±1.0% (±3.0% for the dash 0.25) over the
3.0V to 3.6V operating range, with respect to the
pulse width at the nominal 3.3V power supply.
This holds for all dash numbers. The sensitivity of
the inherent pulse width is nominally -5ps/mV for
all dash numbers.
It should also be noted that the DNL is also
adversely affected by thermal and supply
variations, particularly at the MSL/LSB
crossovers (ie, 63 to 64, 127 to 128, etc).
Doc #06010
DATA DELAY DEVICES, INC.
2
5/8/2006
Tel: [phone] Fax: [phone] http://www.datadelay.com