Hf Square-Wave Response Final Y Amplifier - Fluke Autoranging CombiScope PM3370B Service Manual

CALIBRATION ADJUSTMENT PROCEDURE
7.15

HF SQUARE-WAVE RESPONSE FINAL Y AMPLIFIER

- Apply a 1V/1 MHz square-wave signal with a rise-time faster than 1 nsec to CH1. This signal is
delivered in the 'edge' mode of the calibrator. As an alternative you may use the fast-rise output
of the square-wave calibration generator. Use a 10x attenuator at the end of the cable from the
generator. For reduced channels (0.1 and 0.5 V/div) and EXT TRIG (0.1 and 1 V/div) use a 2:1
(6dB) attenuator.
- Press AUTOSET.
- Put CH1 in 20 mV/div with DC coupled input.
- Select 50Ω input impedance; if not available use a 50Ω termination resistor directly at the
oscilloscope input.
- Adjust MTB/VAR to its fastest position (20.0 or 50.0 ns/div). Small adjustments of MTB/VAR may
be necessary to have a good view of signal details of interest.
- Select the key sequence
'UTILITY > MAINTENANCE >
MANUAL CALIBR' and then
select 'hf y' with the TRACK
rotary .
- Select in succession 'pulse t4',
'pulse t3', 'pulse t2', 'pulse t1'
and 'pulse t0' with the softkeys.
Adjust the pulse top to maximum
flatness and the risetime to the
required value with the ∆ rotary.
The adjustments are a
compromise between fast
risetime and minimal pulse
distortion (aberrations). The
influence of these adjustments
ranges from mid-frequency
(pulse t4) to high-frequency
(pulse t0). The requirement is a
rise-time of ≤ 6ns for 60 MHz,
≤ 3,6 ns for 100 MHz and ≤ 2 ns
for 200 MHz instruments. This
value includes the generator
rise-time. The pulse aberrations
must not exceed + or - 10%.
- Remove the input signal.
- Pulse response and bandwidth
are interdependent: the higher the pulse aberrations, the higher the bandwidth and vice versa. To
check the bandwidth apply a 120 mV/50 kHz sinewave from a constant amplitude sinewave
generator (5500A in mode 'levsine') to CH1.
For reduced channels and EXT TRIG input apply 600 mV / 50 kHz.
- Press AUTOSET.
- Select 50Ω input impedance; if not available use a 50Ω termination resistor directly at the
oscilloscope input.
- Adjust the amplitude of the sine-wave to 6 div exactly.
- Increase the frequency of the sinewave up to 60 MHz (for 60 MHz instruments), 100 MHz (for
100 MHz instruments) or 200 MHz (for 200 MHz instruments) and check that the amplitude on the
screen does not become smaller then 4,2 div.
- Remove the input signal.
- Repeat the bandwidth check for CH2, CH3, CH4 and EXT TRIG input (the bandwidth check for
CH3 and CH4 of PM3392A and EXT TRIG input of PM3390A must be checked via the 10:1 probe
that is delivered with the oscilloscope).
- Remove the input signal.
Figure 7.3 Influence of t4, t3, t2, t1 and t0 on HF square
wave response.
t1=2 ns
t0=8 ns (ABERRATIONS)
t2=5 ns
t3=40 ns
t4=100 ns
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ST6337