Tektronix 1L30, Instruction Manual

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Circuit Description— Type 1L30
Sawtooth
Input
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Fig. 3-4. Block diagram of the sweeper circuit.
The emitters of Q230-Q 240 are long-tailed through R236 to
the — 150 V supply. Current through the sweep comparator
is approximately 3.0 mA.
Sweep
O scillato r. The frequency of the oscillator is
primarily a function of the L (L314J and the C (C314) in
series with the capacitance of D314 in the collector circuit
of Q310. W ith an increase in back-bias across capacitance
diode D314, the capacitance of the diode decreases and the
resonant frequency of the oscillator tuned circuit increases.
The capacitance change is not directly proporational to the
voltage ramp across it; however, high gain in the discrimin­
ator feedback loop reduces this non-linearity.
Frequency modulation of the oscillator is dependent on
the amplitude of the input sawtooth to the capacitance
diode. At maximum deviation, the oscillator sweeps from
225 to 325 MHz.
The output signal from the swept oscillator is tapped across
the partial winding of L314 and oapacitively coupled to
transformers T330 and T331. The transformers provide a
voltage step-up ratio of approximately 2:1 and convert the
single ended input signal to a balanced push-pull output
signal to drive the output amplifier Q340-Q350.
Fig. 3-5 is a simplified drawing of the transformer cir­
cuit. The oscillator is the signal source or generator which
supplies the signal voltage e.
The input windings of T330 and T331 are connected in
series; therefore, the voltage across each winding equals
e /2 {assuming an ideal transformer). The polarity of the sig­
nal at a particular instant of time is as shown in the figure.
This voltage across the input windings will produce an equal
voltage (e/2) across the output windings with the polarity
as indicated.
The generator, or source, is in series with the output wind­
ing for T331; therefore, the voltage at the output equals
3 e /2 with respect to point A. This voltage adds to the volt­
age output of T330 to provide a total output signal of 4 e /2
or 2e.
Fig. 3-5. Simplified diagram of the transformer (T330-T331) cir­
cuit from the swept oscillator to the push-pull amplifier Q 340-Q 350.
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