User guide

13
OPERATING INSTRUCTIONS
TTL/CMOS OUTPUT
The TTL/CMOS output jack provides a fast rise time square wave
output. Either a fixed TTL or a variable CMOS output level is
available. The output is positive with respect to ground and can be
used as an external sync pulse for oscilloscopes or as a variable
frequency signal source for exercising logic circuits. Because of the
fast rise time of this output, cable length should be minimized to limit
ringing and overshoot.
1. Select the desired frequency range and adjust the frequency
controls as required. The OUTPUT LEVEL and DC OFFSET
controls have no effect on the signal at the TTL/CMOS jack.
2. When the CMOS LEVEL switch (13) is OFF, a TTL signal is
output at the TTL/CMOS jack. Select a CMOS signal by
engaging the CMOS LEVEL switch and adjust the level of the
signal by rotating the CMOS LEVEL control (8).
VOLTAGE CONTROLLED FREQUENCY OPERATION
The Model 4011A can be operated as a voltage-controlled generator
by using an external control voltage applied to the VCG INPUT jack.
The externally applied voltage will vary the frequency which is
preselected by the range switches and the frequency controls. Applying
approximately +l0 V with the COARSE control at full clockwise
decreases the output frequency by about 100 times (a 100:1 ratio).
1. Select the desired frequency range and waveform.
2. Set the starting frequency with the COARSE control. Apply a
positive DC voltage to the VCG INPUT jack (9) to decrease the
frequency. A voltage from 0 to +10V will cause the frequency to
decrease by a factor of 100 if the COARSE frequency control is
set at maximum CW rotation. For example, if the starting
frequency is 500kHz, applying +10V will change the output
frequency to 5kHz.
3. To operate the function generator as a sweep generator,
apply a positive going ramp signal to the VCG INPUT
jack. As the ramp voltage increases, the frequency
decreases. The rate of sweep can be adjusted by varying
the frequency of the ramp signal.
4. Specific frequencies can be selected by applying a fixed
dc voltage to the VCG INPUT jack or the frequencies can
be stepped by applying a stepped dc voltage.
5. Do not apply more than ±15 volts (dc or dc + ac peak) to
the VCG INPUT jack. Inputs of more than 15 volts will
not cause any further shift in the frequency and could
cause damage to the generator.
OUTPUT PROTECTION CONSIDERATIONS
Use care when connecting the function generator output to a
signal injection point. Excessive voltage at the point of signal
injection of the function generator can cause internal damage.
Under normal operation, the generator output should never be
connected to an external voltage other than low dc values that
can be matched with the DC OFFSET control. The Model
4011A is overload protected so that shorting the output, even
continuously, will not cause damage. A fuse has been added in
series with the OUTPUT jack to help protect the instrument
from damage by connection to excessive external voltage.
Damage of this type usually occurs by accidentally
connecting the output of the function generator to a voltage in
the equipment under test. The following protective measures are
strongly recommended:
1. The user should understand the equipment under test well
enough to identify valid signal injection points (i.e., the
base of a transistor, a logic input of a gate, etc.). The
voltage at valid signal injection points is rarely high enough
to damage the instrument.