Tektronix 221, Инструкция по эксплуатации

Страница: 15 / 79

Circuit Description—221 Service
TR IG G E R SOURCE
FOLLOWER
Fig. 4-2. Simplified block diagram of the Trigger Sweep circuit.
T rigger/Sweep
The Trigger Sweep circuit performs two functions. The
Trigger portion of the circuit derives trigger signals
internally from the input of the vertical amplifier, or from
signals applied to the EXT TRIG INPUT banana jack. The
trigger output signals are coupled to the Sweep Multi
circuit, which starts the action of the Sweep circuit.
The Sweep portion of the circuit produces a linear
sawtooth output signal when initiated by the Trigger
circuit. The output signal is then amplified by the Horizon­
tal Amplifier circuit for horizontal deflection of the crt. An
unblanking gate signal is also developed that is coincident
with the sawtooth waveform. This gate signal unblanks the
crt to permit a display presentation. An EXT HORIZ INPUT
is also provided so external signals can be applied to the
Horizontal Amplifier circuit to produce horizontal deflec­
tion for the crt. The block diagram of the Trigger/Sweep
circuit is shown in Fig. 4-2. The schematic of the circuit is
shown on diagram 2.
The Trigger Source Follower (Q232A, Q232B) receives
and buffers all incoming trigger signals and couples them
to the base of Q234, one half of a differential amplifier
(Q234 and Q226). TRIGGER LEVEL/SLOPE control R213
sets a reference voltage level that corresponds to a desired
trigger point on the incoming signal. This voltage is
coupled through Q212 to the base of Q226, the other half
of the differential amplifier. Transistor Q214 provides a
slope switching function in conjunction with Trigger
Slope Selector transistors Q216 and Q218. When
TRIGGER LEVEL/SLOPE control R213 is rotated, the
resulting voltage applied to the base of Q222 causes it to
saturate at about the mid-point, or a zero volt level of the
control. At this point Q214 turns on and slope switching
occurs through Q216 or Q218.
REV. B, AUG 1974
4-3