Coarse And Fine Offsets; High Frequency Adjust Signals - Tektronix 11A52 Service Manual

Theory of Operation
the address of the voltage to be read; and the analog readback is the FBOUT signal. Readback is possible only
when the EN2 line is low.
Assembly AlAl provides offset voltages DC balance for each channel; A1A2 provides variable gain, HF Adjust
and input current null voltages.
Coarse and Fine Offsets
Coarse and Fine Offset voltages are available for the two main amplifiers U310 and U410 and any external
TEKPROBE™ accessory.
The main amplifier input offset voltages are generated by the ACVS and are divided by the resistors R542,
R544, R547, R546, R543 and R545. Probe-offset voltages are also generated by the ACVS; they are divided by
R663, R662, R661, and R660. Diodes CR655, CR651, CR656 and CR652 clamp any static voltages introduced at
the TEKPROBE™ connector.
In the 11A52 the main amplifier offset and the probe offset are driven by separate ACVS outputs. When an
active probe with a TEKPROBE™ connector is used, the probe offset output is driven by the ACVS and the
main amplifier receives no offset voltage. When a non-active probe is used, the offset voltage is applied only
to the main amplifier input; the probe offset output is not driven.
In each amplifier channel the COARSE offset is designed to be 20 times larger than the FINE offset. The
BALANCE lines are used to correct both input and output offset voltage errors in the main amplifiers. The
typical maximum voltages available to the main amplifiers from the COARSE, FINE, and BALANCE controls
measured at L210 and L530 are as follows:
COARSE=
FINE=
BALANCE=
±1.0178
v
±0.0506
v
±0.0629
v
Components L210, C210, LR210, L530, C520, and LR520 filter noise generated by the Sample/Hold module
(AlAl).
High Frequency Adjust Signals
The HF Adjust outputs from A1A2 control the transient response of the two main amplifiers. An incremental
positive voltage at A1A2 pin 15 or 17 will cause more overshoot in the transient response. The HF Adjust
signals are set for optimal transient response of the display signal path at each gain setting. The trigger signal
path is identical to the display path; their High-Frequency Adjust inputs are both connected to the same node
in the adjustment network. (See pins 21and24 on U310 and pins 24 and 27 on U410.) The auxiliary signal paths
require slightly reduced peaking, obtained by resistors R326, R327, R328 and R329. Also, CR235 and U335 add a
temperature-dependent voltage to the HF Adjust signals. Inverters U335A and U33SB send the CH 1 HF Adjust
and CH 2 HF Adjust signals to U310 and U410, respectively.
11A52 Extended Service Manual 2-15