628
6 Reverse Engineering of Microcircuits
it is impossible to recover the correct electrical circuit of such protected microcircuit. These and similar other protected solutions were implemented in the S84 series
microcircuits designed and produced at the Integral plant in Minsk. These microcircuits were withdrawn from production over ten years ago and replaced with the new
IC generation, where similar but different special technical solutions were applied.
6.8.2 Non-standard Elements of Protection of Bipolar
Microcircuits from Electrical Overloads and Static
Electricity
Growth of the integration level, reduction of geometrical dimensions of active regions
and bipolar transistors lead to a reduction in breakdown voltages of microelectronic
product devices. One of the results is an increase in the danger of failures associated
with the effect of electrical overloads from various sources during production and
operation of products. Static discharges, voltage, and current pulses in metering and
test stations and during operation as part of the onboard radio electronic equipment
cause destruction of p-n-transitions, gate dielectric, and other structures sensitive to
the effect of overloads.
Destabilizing factors that significantly affect workability of bipolar LSICs first
of all include the phenomena of electrostatic discharge (ESD)—unauthorized pulses
of voltages (currents) of positive and (or) negative polarity affecting LSIC or power
circuit outputs.
The most common method of protection is ensuring optimal conditions for the
discharge current of an electrostatic charge (ESC) or an interference impulse to the
zero or positive output of the supply voltage source.
Such a classic (standard) method of protection is the placement of the back-on
diode or diode and diode-resistive ESD protection circuits on all of the LSIC outputs.
One of the authors of this book has developed and implemented in LSIC, a number
of effective protection circuits based on using known physical effects occurring in
a bipolar transistor operating in the mode with a floating base potential. An additional but equally important function of these elements was ensuring protection from
copying of microcircuits including this element.
Figure 6.98a shows the simplified equivalent diagram explaining the general principle operation of this non-standard device for LSIC protection from ESD and positive voltage bursts by forming a low-resistance circuit of discharge to the common
bus. The circuit contains a connected pair of n-p-n transistors VT1, VT2, the first
one—with fixed potential (grounded through R), the second one—with floating base
potential. When the positive voltage impulse of the V = f (t) noise (or ESC potential)
appears at the protected output at the moment t 0 , as shown in Fig. 6.98b, the transistor
VT2 included according to the circuit with a floating base (voltage V 1 ) is the first to
enter the avalanche breakdown mode of the collector–emitter circuit at the moment
t 1 . The current I
12
CE in the circuit t of the emitter VT2 forces the voltage at the resistor
6 Reverse Engineering of Microcircuits
it is impossible to recover the correct electrical circuit of such protected microcircuit. These and similar other protected solutions were implemented in the S84 series
microcircuits designed and produced at the Integral plant in Minsk. These microcircuits were withdrawn from production over ten years ago and replaced with the new
IC generation, where similar but different special technical solutions were applied.
6.8.2 Non-standard Elements of Protection of Bipolar
Microcircuits from Electrical Overloads and Static
Electricity
Growth of the integration level, reduction of geometrical dimensions of active regions
and bipolar transistors lead to a reduction in breakdown voltages of microelectronic
product devices. One of the results is an increase in the danger of failures associated
with the effect of electrical overloads from various sources during production and
operation of products. Static discharges, voltage, and current pulses in metering and
test stations and during operation as part of the onboard radio electronic equipment
cause destruction of p-n-transitions, gate dielectric, and other structures sensitive to
the effect of overloads.
Destabilizing factors that significantly affect workability of bipolar LSICs first
of all include the phenomena of electrostatic discharge (ESD)—unauthorized pulses
of voltages (currents) of positive and (or) negative polarity affecting LSIC or power
circuit outputs.
The most common method of protection is ensuring optimal conditions for the
discharge current of an electrostatic charge (ESC) or an interference impulse to the
zero or positive output of the supply voltage source.
Such a classic (standard) method of protection is the placement of the back-on
diode or diode and diode-resistive ESD protection circuits on all of the LSIC outputs.
One of the authors of this book has developed and implemented in LSIC, a number
of effective protection circuits based on using known physical effects occurring in
a bipolar transistor operating in the mode with a floating base potential. An additional but equally important function of these elements was ensuring protection from
copying of microcircuits including this element.
Figure 6.98a shows the simplified equivalent diagram explaining the general principle operation of this non-standard device for LSIC protection from ESD and positive voltage bursts by forming a low-resistance circuit of discharge to the common
bus. The circuit contains a connected pair of n-p-n transistors VT1, VT2, the first
one—with fixed potential (grounded through R), the second one—with floating base
potential. When the positive voltage impulse of the V = f (t) noise (or ESC potential)
appears at the protected output at the moment t 0 , as shown in Fig. 6.98b, the transistor
VT2 included according to the circuit with a floating base (voltage V 1 ) is the first to
enter the avalanche breakdown mode of the collector–emitter circuit at the moment
t 1 . The current I
12
CE in the circuit t of the emitter VT2 forces the voltage at the resistor