Sine Shaper-Unit U4 - Philips PM 5167 Instruction Manual

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By setting switch SINGLE SHOT MODE from SET PHASE to START, a trigger pulse appears at U5/513 to
set the fl ip- flop.
Diode U5/ 419 avoids multiple triggering as a re sult of bouncing contacts of switch START.
The flip-flop can also be set by a negative voltage jump of 5 V at the CONTROL INPUT (connection
U5/ X
=
O V) . Due to this a voltage is available at connection X and the oscillator is start. However, the first
positive-going square-wave resets the flip-flop again, so that oscillation stops af ter one cycle .
Potentiometer SET PHASE is adjusted by means of potentiometers U5/679, 682.
U5/682 serves to adjust the positive part and U5/679 the negative part of the square-wave . Both adjusting
operations are interdependent.
3.1.4_ Sine-shaper Unit U4
The sine-shaper consists of :
- a diode-resistor network
- a circuit for peak compensation
- a delay section to start peak compensation at the right time
- an inverting wide-band amplifier
3.1.4.1. The diode-resistor network fig. 22 converts a triangular signal of lOV pp into a sine-wave signal with an
ampl itude of 5V . 2/rr
=
3,18 V.
Each diode (U4/401 to 414) is biased by a different voltage from one voltage divider each (U4/601, 604 to
619 and 603, 606 to 621) .
They function as amplitude-dependent switches and are increasingly connecting in paralIei with resistors
U4/ 605, 608, 611 , 614, 617 and 620 at rising triangular voltage. Magnitude and symmetry of the d iode bias
is determined by two voltage sources U4/351 and 313 to 315, which are coupled to better the temperature
compensation. Adjustment is performed by means of U4/666, 669 .
The diodes with the highest bias voltage U4/413 and 414 serve to form the sine-wave tops. They shou Id form,
together with the corresponding voltage source, an extremely low-ohmic current path. As this only can be
approximated due to the forward resistance of the diodes, the peaks obtained are cut-off by a compensating
ci rcuit.
3.1.4.2. The peak-compensating circu it consists of transistors U4/301, 302, 303 and 305.
Diodes U4/413, 414 are biased by U4/301, 302 in such away, that they only conduct during the period the
tops of the sine-wave are formed.
The peak compensation takes over the current by means of transistors U4/301 and 302 respectively via diodes
U4/413 and 414 . Stages U4 / 303 and 305 respectively ampl if y and invert the current, which is then supplied
to the summing point at resistor 640.
3.1.4.3. The delay circuit in signal path U4/504 to 506; 636,751,752 compensates the phase delay of the peak
compensation at frequencies higher than 1 MHz.
Due to its low-pass characteristic this delay circuit causes the distortion facto r to be decreased for frequencies
higher than 1 M Hz .
3. 1.4.4. I n wide-band ampl ifier U4/307 to 312 the voltage loss of 2/rr caused by the sine-shaper is compensated by
amplifying V
= -
rr/2.
Consequently the sinewave signal at the output has the same peak value as the triangular input voltage.
The DC-offset of the output voltage is adjusted by U4/644, while the frequency response for range 1 to 10 MHz
is adjusted by U4/508.
3.1.5. Power amplifier Unit U6
The power ampl ifier fig. 22 is complementary and symmetrically arranged and contains:
- an emitter-follower stage
- a voltage-amplifying cascode part
- a driver stage
- an A/B - power output stage U6/309, 310
- elements for a DC OFFSET-control
- an OVERRANGE indicator
-