6.8 Practical Examples of Implementation …
631
6.8.3 Non-standard Elements of Protection of Output Stages
of Microcircuits with Schottky Diodes
Non-standard output adapting components (AC) of LSIC Schottky TTL increasing
IC protection from reverse engineering are based on the widely known push–pull
signal amplifier (SA) circuit with TTL levels shown in Fig. 6.100.
To coordinate amplifier circuits by signal levels with internal gates, developers
usually use additional matching circuits (MC). The main options of such standard
solutions are shown in Fig. 6.101b–d. The integrated matching circuit and the amplifier circuit form the output AC with the active output, since load capacitance is
charged and discharged by switching active ACs—output transistors VT2, VT3. In
enable state, AC is characterized by low-level output voltage:
U
AB
oL = U
V T 3
K E H + I oL · r K ,
where r K is the resistance of the collector of the output transistor VT3.
Output characteristic of the AC in enabled state corresponds to the curve 1 in
Fig. 6.102. Output ACs of LSIC Schottky TTL are distinguished by an increased
output voltage U OL = 0.3–0.35 V, which is due to an increase in the residual voltage
of the open output transistor VT3 due to application of a parallel Schottky diode in
it:
U
∧ o − −Γ % 0.75V − 0.55V = 0.2V.
In disabled state, AC is characterized by high-level output voltage:
I, U
AB
O H ≈ U αC − U
V 12
B9 − U
V D
I P −
O H
β
V T 2
N
R1.
Output characteristic of the AC for disabled state corresponds to the curve 2.
Standard value of the 2B parameter. In LSIC Schottky TTL, it is often
necessary to apply output ACs which, in addition to two active states with voltage
levels U 0H , U 0L , shall contain a third state, which is implemented by means of
an additional control EN in by low voltage supply. In active states, output levels
correspond to output levels of ACs with active outputs, while output characteristics
correspond to curves 1 and 2 in Fig. 6.102. In the third (passive) state, the AC
is characterized by output currents I 0ZL , I, which are leakage currents of closed
transistors VT2, VT3, while the output characteristic corresponds to the curve 3 in
Fig. 6.102.
In the circuit shown in Fig. 6.101, only one active element of load capacitance
discharge is present (transistor VT2), while the AT output here is formed by its
collector. In disabled state, high-level output voltage is formed due to the external
power source U L and the load resistor R L :
631
6.8.3 Non-standard Elements of Protection of Output Stages
of Microcircuits with Schottky Diodes
Non-standard output adapting components (AC) of LSIC Schottky TTL increasing
IC protection from reverse engineering are based on the widely known push–pull
signal amplifier (SA) circuit with TTL levels shown in Fig. 6.100.
To coordinate amplifier circuits by signal levels with internal gates, developers
usually use additional matching circuits (MC). The main options of such standard
solutions are shown in Fig. 6.101b–d. The integrated matching circuit and the amplifier circuit form the output AC with the active output, since load capacitance is
charged and discharged by switching active ACs—output transistors VT2, VT3. In
enable state, AC is characterized by low-level output voltage:
U
AB
oL = U
V T 3
K E H + I oL · r K ,
where r K is the resistance of the collector of the output transistor VT3.
Output characteristic of the AC in enabled state corresponds to the curve 1 in
Fig. 6.102. Output ACs of LSIC Schottky TTL are distinguished by an increased
output voltage U OL = 0.3–0.35 V, which is due to an increase in the residual voltage
of the open output transistor VT3 due to application of a parallel Schottky diode in
it:
U
∧ o − −Γ % 0.75V − 0.55V = 0.2V.
In disabled state, AC is characterized by high-level output voltage:
I, U
AB
O H ≈ U αC − U
V 12
B9 − U
V D
I P −
O H
β
V T 2
N
R1.
Output characteristic of the AC for disabled state corresponds to the curve 2.
Standard value of the 2B parameter. In LSIC Schottky TTL, it is often
necessary to apply output ACs which, in addition to two active states with voltage
levels U 0H , U 0L , shall contain a third state, which is implemented by means of
an additional control EN in by low voltage supply. In active states, output levels
correspond to output levels of ACs with active outputs, while output characteristics
correspond to curves 1 and 2 in Fig. 6.102. In the third (passive) state, the AC
is characterized by output currents I 0ZL , I, which are leakage currents of closed
transistors VT2, VT3, while the output characteristic corresponds to the curve 3 in
Fig. 6.102.
In the circuit shown in Fig. 6.101, only one active element of load capacitance
discharge is present (transistor VT2), while the AT output here is formed by its
collector. In disabled state, high-level output voltage is formed due to the external
power source U L and the load resistor R L :