- Project Runeberg -  Elteknik : Tidskrift för elektrisk kraftteknik, teleteknik och elektronik / Årgång 2. 1959 /
103

Table of Contents / Innehåll | << Previous | Next >>
  Project Runeberg | Catalog | Recent Changes | Donate | Comments? |   

Full resolution (JPEG) - On this page / på denna sida - A Linear Selection Memory with Transistor Driving Circuits, by Bengt Jiewertz

scanned image

<< prev. page << föreg. sida <<     >> nästa sida >> next page >>


Below is the raw OCR text from the above scanned image. Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan. Ser du något fel? Korrekturläs sidan nu!

This page has never been proofread. / Denna sida har aldrig korrekturlästs.

Fig. 3. a) Selected word with transistor gates,
b) Drive circuit of transistor gate.

at a constant collector current /<> The resulting
static dissipation of the collector and base regions is
a function of the base current 1B and has been chosen
at the minimum value (Pc + Pßhn- During the
switch-over times A t± and A f2, fig. 4a, the current I c
and the drive voltage Vd give additional collector
dissipation Pc (A t J -f Pc (A t2) with a peak
amplitude more than about ten times the saturation value.
The peak currents at the base also introduce
dissipations PB and PB (t) which are functions of the
on and off time constants t1 and U of the base circuit.
The total mean dissipation PT during a pulse period
with the length 2 f0 is then

2 t0

Pt== YFo i(Pc + Pb) -{to ~ A tl ~ A h) +j\Pc (A tl) +

0

+ Pc (A h) + PB (f,) + PB (*,)] dt}

The dissipation during the off state is neglected.
At high repetition rates the switch-over dissipation
peaks give appreciable contributions to the total
dissipation. In fig. 4b is shown how the total
dissipation PT increases when the repetition period
decreases. The switch-over peaks have been calculated
from measured curves showing the current and
voltage variations versus time at the base and
collector. As transistor parameters change with
temperature, a better knowledge of the dissipation is
obtained from measurements of the junction temperature
at actual operation of the transistor. In fig. 4b is
also shown a curve of the junction temperature
versus repetition period.

Calculations of the power dissipation of the output
transistor of the drive generator show that four
transistors must be connected in parallel. In the
gate transistors no power peaks are obtained but

the full current gates Aj and AjR must have two
transistors in parallel. For the write current gate Ajw
only one transistor is needed. This number of
transistors makes it possible to operate the circuits at an
ambient temperature of 60°C with a junction
temperature less than 75°C. Compared to a
coincident current memory of the same size, constructed
according to similar principles, a linear selection
memory needs about 75 per cent more transistors
in the address gates.

The diode in a read wire is also passed by a full
current pulse. Measurements on several diode types
show that a power peak at the beginning of the
pulse must be added to the static dissipation.
Germanium diodes of the type 0A9 proved to be suitable
for use at an ambient temperature up to (50°C.

Temperature working range

A linear selection memory is working at the
coincident current principle during the write phase. The
temperature working range of a memory can be
determined after the same principles as for a
coincident current memory". Calculation of the margins
of the write and help currents in the actual
memory due to component and temperature
variations give a total tolerance of A Im — 25 mA at 60°C,
when a temperature compensated drive current is
assumed.

A core in a linear-selection memory is always
disturbed by at first one write current pulse, 0.5 Im,
followed by a number of help current pulses 0.5 lm.
The disturb pulse program at core testing is for that
reason composed of one pulse writh an amplitude
somewhat larger than 0.5 lm followed by pulses less
than 0.5 ///,. Only two currents coincide in contrary

Fig. a) Collector current pulse.

b) Power dissipation (Pt) and junction
temperature (Tj) as functions of the repetition rate.
Tj is the average value of five transistors 2N317,
max. diff. 20°C. Ambient temperature 40°C.
Pf is calculated from measured waveforms at
Wi = 15 volts, Ir = Wi mA and A tx = A t.2 =
= 0.1 jus.

ELTEKNIK 1959 1 103

<< prev. page << föreg. sida <<     >> nästa sida >> next page >>


Project Runeberg, Sat Dec 9 22:19:30 2023 (aronsson) (download) << Previous Next >>
https://runeberg.org/elteknik/1959/0107.html

Valid HTML 4.0! All our files are DRM-free