~
l'1li ANALOG
1.2-BitDe'glitched
e OutDIAConverter
DEVICES
FEATURES
Registers. D/A. Amplifier in Single Hybrid
Deglitched Voltage Output
6MHz: Update Rate
HDD-1206 FUNCTIONAL
BLOCK DIAGRAM
APPLICATlONS
Vector Scan Displavs
Analytical Instrumentation
Digital VCOa
Military Systems
OBS
OLE
GENERAL DESCRIPTION
The i\naJog Devices HDD-1206 D1:'\converter combin~" innovative design techniques with remarkable hybrid construction
to achieve deglitched \'oltage outputs at
update rates as
as 6MB",
Despite its small sizc and low power, the HDD-J206
the user with a complete solution h) demanding
which require the conversion of high-speed digital
dcglitched analog output voltages.
into
and
The unit is housed in an industry st:mdard
contains all the necessary circuit components to
outpUts at high update rates witbout the need for
external circuits, Input registers, current-output DiA, deglitching
circuits, and an output amplifier arc aU included inside the
HDD-1206,
With the deglitcbing problem solved in a
the
user of the HOD.1206 is able l(!
the SQlulioniow
his system with a minimum of
effon. User involvement
is limited to thl: simpk task of establishing the "hold" time for
an optimum value by sclel:ting the correct resistor value.
filtl:r
After that step is :u:complished, the addition of 3
at the output of the VIA assures a ".:;k3n"
of tbe 12 bib of digital information applied 10 the input~ at
video update rates,
The HDD-1206 is available in 32-pin dual in-line ceramic
packages.
--------
PIN DESIGNATIONS
HDD-12()6
TE
SPECIFIC IONS(typical
Mudd
+ 25"Cwith nominalpowersuppliesand1kfl outputloadunlessotherwisenoted)
HD1).t2~M
HDO.UMJW
MJn
~tu
RESOLUTION
w
Am
Typ
11
2,5
Typ
Am
t <tOI2S
A('-CURACY (Uncarity)
DiffcrcnWJ Nonlinearity
Zero OIlKI' (IniWJ)
~ 35
GU.itanlccd
5(J
TEMl'1!1LI\ TURECOI!FFIClENTS
5
W
100
LiDCarilY
G.in
ScutmgTlfDC 10 'I/I.$B
.:.5, I2V FSCh"ngc
rrmPC
2
bO
SI}
2S
Adju".hlc
OBS
Slew IUIC
Gain
~
ns
'"
'ITUS)
+2.4
0
"0"
(S«
TaMI ""I", ,"'gr',
STROBE ISI'tJT
TfL
"I}"
Load
RIi!ClimcihH!I!nc[IO%-?O%)
\\('!ath
,2,4
(I
15
,!»:wo"lrah:' .
h
I,0000
v
v
rfl.!,,"d
'"
'"
MHz
v
V
l.5&
010 " 5,12
Curren!
RH' l,O()OO
Ilipol.. Vollage
Currel>!
R!:"ana!Glllch
Ourpul
V
lTL)$') J d
TE
-5
+(14
Oll< $1.",1..0
$0
v
OLE
OncS"",dord
Lo..a (cach hi 0
Coding
""S
+0.4
~
iliA
, 512
5U
(II
1,000
V
lOA
mV
(J
100
I
1'1'
lOA
lOA
mA
",';}!V
';\i
IW
0
"C
-125
5>
'IHI'.RMALRE$!STANCE'
H
B
.cw
'('/\1;'
MTBP'
3.015
Hmlf~
lIDO, 1206J""
HDrJ..120h$M
UUJ!I
W'C
14 '<1f
,,",l/t><,n(,."",."".
~~
THEORY OF OPERATION
The equivalent circuit for the for the HDD-1206 D/A converter
is shown in functional block diagram.
The unit consisTSof input registers, fast-SCHIIDgcurrent
DII\, output amplifier, timing generntor, aDd ass{ICiared
The purpose of the input register circuits is to de-skew the
inpUt bits and assure Their simultaneous arrival at the inpul of
The curren! O/A. This is critkal b<."C3use
time skew on the input
data bils is a major contributor to discontinuities, or
"
in the analog output of a OIA.
The Timing Generator includes a Track & Hold circuit and
generates the required internal pulses for operation whenever it
receives a Strobe input pulse. See
I, t.he HOO.1206
timing diagrnm.
OBS
STRO6t
HOW
TRACK
1
1
I
HLGi$IER
To.. -I I J ~OlC
!iI..r I
SAM!AS
MAX
olm""
Figure
1, HDD-1206
Cfumgfng!
TimIng
DIagram
DrA CONVERTERS
verters may be a useful approach to
of the HDP-1206 unit.
the operation
OiA converters are inherently fa$lcr than
voltage-output types hecausc of ttIe absence of an
This mean$
converters have no slew rate limitation which can slow settling; not are Theysubject to the overshoot
and
problems often associated with feedback
Bmh current-switching and
converters display a
discontinuity, or "glitch," in their
output$ because of the
basic characteristic of satUrated logit: (rrL is an example) which
causes the
delay to be less for negal
than il is for
inputs.
This difference in propagation
manifests itself as a "worst
case
at the major C'arrypoint. or mid-scale, of the OUtpUI
range of the .::urrent converte" This is the
at which nearly
equal and opposite .::urrems arc being switched within the
converter.
"T'
1+,
CURRENT.OUTPUT
A brief reviewof the salient characteristicsof current DrA con-
ROLIt
OLE
(DIgital
L-
Inputs not
As shown, the Strobe pulse is a positive-going 1'1'1. pulse supplied
by the user of the HPO-1206. Internal timing circuits establish
the maximum 55ns delay from the leading edge of the Strobe
pulse to the leading edge of the T/H (TrackiHold)
and
the maximum IOns dclay from the
edge of the
pulse to the leading edge of the Register pulse. The data from
Ihe input
are strobed int.o the current D/A at the end
of Ihis 6Sm interval, so
must be valid by that tinle.
The user determincs the width of the T/H pulse (and the Register
pul~e) by select.ing the value of the RUDLDresistor. St'C
I and 2. As shown, the width uf the Hold pulse can vary from
approximatcly 30ns to approximately lOOnsby using resistOr
values from Ik 10 5k, respectivel)'.
The "glilch" at mid-scale, the switching point of the Most
Bil (MSB), will be halved at the !I. and 3;'
halved again at The and %
etc, The
of the
is a function
si2nal dynamks and caonot
TE
The variations in
caused
dynamics
create a multitUde of illlermodulation (1M) products, some of
which fall imo the video
as 1>purious
and
increased noise level. These 1.\1
arc also relatively
immune to elimination by
The amplitude of the glitch can be reduced by
the
bits; bur no amount of dc-skewing or
can negate
the physics nf sarurated logic which cause Ihe glitch to be
initially.
The heS!
then, is to cause the glitch to remain a constant
across the entire outpUt range of the converter. The efficiencies
of Ihe circuit will be enhanced if the solUtion can also permit
the full drive capabilities of the currcnt-outpul DiA in
either unipolar or bipolar modes of
The design approach used in the Analog Devices HDP-1206
DiA converter accomplishes these desired goals and
voltage OUtpUtsat bigh update rates.
NOTES ON OEGLlTCHING
Refer again to the equivalent circuit for the HDD-1206. The
data bits are applied thmugh the input register to the current.output PIA converter, which is capable of
up to 5.l2mA
of ~'\!IpUtcurrent.
The oUtput of the currern D/.'\, in rum, is applied to the
of the OUtput
via
external 10 the HDD-1206.
The Timing Generator supplies the necessary
and
to apply signals to the current D/A and OUTputamplifier after
the initial glitch caused by the digital inpUts has subsided.
~
Figure 2, Hold TIme vs. RHolD
For most applications, a value of 3.6kH and a pulse width of
approximately 85ns is the optimum choke, This pulse width
wiIJ "hold" the analo~ oUtpUt of the HDD-1206 OiA uOli! the
"glileh" resulting from the most recent update has passed.
without infringing on Ihe word rate capabilitie$ of the
HPP-1206.
The digital "I" (Hold) level of the TIH pulse CaOSC$the switch
at the input Qf the amplifier to open, holding the last value uf
tbe current DlA con\'erter. During this hold inten'al,
transients c;wsed by updating digital inputs arc masked from
the amplifier, thereby avoiding HDD-1206 output discontinuities
whose amplitUde would be a function of signal
Ten nanoseconds after the 'fiH pulse goes ({)the
"I"
the register pulse also changes stare frum "0" tQ "I".
--
----
This tr.msition moves the output of the current PIA to the new
value established by the most recent digital inputs applied to the
HPP-1206.
. '.'
!lIT, ,...", Q
." ~
t:
'
.
0fI1
...
Off' ,
..,. ~,
As shown in Figure I, the oUlpUt of the HPP-1206 will contain
switching transients associated with the T/H pulse, But these
"glitches" will be conslilOr in amplitude and duration and will
occur at the update rate, since they are a function of the Strobe
pulse applied by the user.
0."
...,~
""",...
...""Q<j
WTPOf
CON\lV!TEA
..,.~
""QJ;
..' ..@
..,"~
...""...~
, ru:
..v
"
"...~)',..,'
These switching tr.msicms will settle out io approximately 500ns,
and will have uniform amplitUde over the complete analog output
range of the D/A. For strobe rates of 2MHz and above., the
Sl.:ttling interval switching from "hold" to "track", and vice
versa, will produce a constant de offset on the output. The
HPD-1206 is not intended to get rid of all glitches per se; it is
designed to provide a constant-amplitude glitch.
OBS
I) n.. ..,..,
"""._"""""""-0<ft'PVt.
,..,. 1ruro
-,..........-..
"...,.--
Figure 4, HDD.1206 Blpo/ar Cormac/ions
The output voltage swing is established by the value of feedbAck
resistor R..'S. The table below indicates output levds for both
unipolar and bipolar operation, with feedback resistOrs of either
1,000n or 2,0000.
When the area under the transient curve is held constant, the
frequcncy spectrum of the glitch is a fine Ime, i..e" a single-l.ine
spectrum at the sample rate frequencies, and harmonics of the
sample frequency.
OLE
Hold resistor RHow COlUtcctc.'dbetwc.-enthe + S\' supply and
Pin 31 sets the width of the Hold mode of the TIB pulse. Test
Point Pin 2 is used for observing the pulse.
The HDD-1206 effectively e[Jminates the 1.\'\ product.~ discussed
above. When it does, the signal-tn-noise (SIN) ratio approaches
that of an ideally-quantizcd signal, where the rms noise is
qlVU, when frequencies above Nyquist arc fillered out.
VS. PEDESTAL
The Offset Adjust potentiometer is used to set the desired analog
output of the HPD-1206 and can be used to help assure correct
volta.ges arc prc.'SCrllwhen the DIA ismsta.Hed in the system,
TE
When operated in a unipolar mode with digital "0" applied to
all inputs but no continuons strobe pulses applied, the Offset
Adjust is set for an analog output of - 5.l2V or less lLSB, with
Ik for the value of Rf'U' (NOTE: At lea.st one strobe pulse
needs to be applied to latch the input data into the registers,)
In addition to the "glitch" which is a characu:risue of current
D/As, the t['dck & hold used in the HDD-1206 also contributes
an anomaly to the OUtput signal.
Refer to Figurc 3. This diagram compares the "glilch" created
by the HDD-1206 to the pedt"Stalcreated by the internal T/H
circuits.
If the HDD-1206 is installed in a. system and the strobe pulse is
applit-d. continuously, the Offset Adjust is calibratcd for the
desired oUtpUt value with a digital "0" applied to all input pins.
r
HI""'"
---~'h,_. """""
""'eM<""
,
,
.'I"
~~
~
Any change in rhe current PIA output has stabJi7.cd by the time
the TIH pulse remInS to the digital "0" (Track) leYel. Re-esrab.
lisbiog the tr.!ck mode closes the switch at the input of the
amplifier and the omput of the HPP.1206 move... to the neW
analog value diclated by the digital input word.
GLITCH
,..
'h'
~
HDD.1206 ANALOG OUTPUT WITH IkO LOAD
-.""....
."no.".. ,'.N""'T
Digital
Inputs
Figure 3. Pedestal/Glitch
Relationship
As shown, the "glitch" is a transient signal which remains constant
in width and amplir.ude over the entire outpUt range, at all
update rdtes, Thepedesta!, on the other hand, is IIf1offset signal
whose amplitude can v.ary (because of switching transient settling)
as a function of hold time and word ratc.
! II. ""III
III.
110
I 10
""IHIO
101.. III
100. .000
011. .1 t I
010...000
00 I.. . III
000. .001
000. ..000
This pedestal is caused by charge transfer associated with the
hold capacitor; the transfer occurs when the HDD-1206 circuits
arc switched from a "track" to "hold" condition. The pedestal
is basicallj' an (,ffset error in the HDD-1206 output and can be
compensated with the Offset Adjust when the unit is installc:d in
the user's system.
Complementary
Offset Binary (COR)
BipoiarOUlPUI
RvlI;:; 2k
Complementary Binal)' (CRN)
Unipc!ar Negative Output
R~'1' '" Ik
0.0000 (0)
+5.12(+FS)
+5J17S
"" ()JJGX.?;(! lLSB)
U781;
.. L5t.25 ( till'S)
.~2.56
USdA
.. .1.55875
+0.0015(" IUB)
.. 2.560'2)
0.0000
- 3.83875
-15575 ( )i2FS)
.. 3.84(3i4,
-2.56
::1.1175
.. 5.1150
-5.1.175
JiS -"ILSB:
5J1875(FS.. !LSB)
-
ORDERING INFORMATION
Model HPD-1206JW PIA converter is housed in a ceramic
package, the model HDD-1206SM is a hcrmetkaUy scaled version;
outline dimensions arc shown dsewherc.
Figure 3 is not drawn to seale; there is no attempt to imply the
identified elements have precisely that relationship to one another.
They arc exaggerated f()r illustrative purposC'S.
Applicati:ons
Mating individual pin sockets are available from AMP. Part
number 6--330808.0 are knockoUt end type; 6-330808.3 are open
end type.
Bipolar conn«:uons for the HDD-1206 D/A converter are shown
in Figure 4. As indicated, a unipolar negative Qutput is accomplished by COtmccting Bipolar Pin 29 to ground, instead of to
Pins 27 and 28.
-