634
6 Reverse Engineering of Microcircuits
Fig. 6.101 The most commonly used 2-cycle circuit of the signal amplifier of the active output AO
of an IC Schottky TTL (a) and equivalent variants of outputs (b–d)
Output characteristic of the AC in this state corresponds to the curve 2 in Fig. 6.102.
In disabled state, low-level output voltage is formed due to the load resistor R L .
Let us consider circuitry of output ACs of the AO type designed to be used as
effective means of protection from reverse-engineering attempts.
The circuit of the output AC as shown in Fig. 6.103a in case of using a basic
resistor as the Z 0 discharge element has a reduced high-level output voltage of U QE .
Since the voltage supplied to the AC input from the internal blocks of the LSIC has
the end value and U = 0, the phase-separating transistor is in the active mode, and
the voltage at its collector is reduced by the following value:
AU K = (11, −1/%)
∧
K 2Q
6 Reverse Engineering of Microcircuits
Fig. 6.101 The most commonly used 2-cycle circuit of the signal amplifier of the active output AO
of an IC Schottky TTL (a) and equivalent variants of outputs (b–d)
Output characteristic of the AC in this state corresponds to the curve 2 in Fig. 6.102.
In disabled state, low-level output voltage is formed due to the load resistor R L .
Let us consider circuitry of output ACs of the AO type designed to be used as
effective means of protection from reverse-engineering attempts.
The circuit of the output AC as shown in Fig. 6.103a in case of using a basic
resistor as the Z 0 discharge element has a reduced high-level output voltage of U QE .
Since the voltage supplied to the AC input from the internal blocks of the LSIC has
the end value and U = 0, the phase-separating transistor is in the active mode, and
the voltage at its collector is reduced by the following value:
AU K = (11, −1/%)
∧
K 2Q