Figure 5-4. Two-input bistable stage, +6-volt clamped output, schematic diagram and logic symbol

TM 11-5805-424-15/NAVELEX 0967-220-9010/TO 31W2-2G-41

Figure 5-4. Two-input bistable stage, +6-volt clamped output, schematic diagram and logic symbol

Rb). Resistor Ra serves as a limiting resistor. If

type (d above), except that when the FFB-type

either input is a high level (ground), the

transistors conduct, the output is held at +6 volts instead

applicable diode conducts, providing a high

of ground, and no limiting resistor is used in the input

level (ground) at the output, with resistor Rb

circuit of transistor Qb.

dropping the 15 volts from the supply.

5-8. AND Gate Stages

(2) In the GAS-type AND gate (B, fig. 5-5),

(fig. 55)

capacitor Ca differentiates its input square wave,

and diode CRa passes only the positive spike if

the input to resistor Ra is also a high level. If

a. General. Four basic variations of AND gate

the input to resistor Ra is a low level, capacitor

stages are used in the equipment. Two are inverting

Ca can never charge above ground and no

gates and two are noninverting gates. Since the

output is available.

function of the stages is essentially the same, the same

(3) Two GAI-types of AND gate are used in the

basic logic symbol is assigned every stage. Differences

equipment.

in the logic symbols denote whether the required inputs

to activate the stage are low level (circle at the inputs of

(a) The type shown in C, figure 5-5, requires

the logic symbol) or high level (no circle at the inputs),

two high-level inputs (ground) to hold

and whether the activated (enabled) output is low level

transistor Qa cut off, providing a low-level

(circle at the output of the logic symbol) or high level (no

(-15 volts) output. A low level applied to

circle at the output).

either input is passed by its appropriate

diode (CRa or CRb) to the base of

b. Circuit Analysis. An AND gate will develop a

transistor Qa, turning Qa on and providing

proper output when coincident input pulses of the same

a high-level (ground) output. Resistors Ra

polarity are present on the input lines.

and Rb provide initial bias for the

(1) The GAD-type AND gate (A, fig. 5-5) requires

transistors. Resistor Rc

the two low-level inputs which are blocked by

diodes CRa and CRb, in order to provide a low-

level output (no current flows through resistor

Change 5

5-7