Tektronix P6249 User Manual

Theory of Operation

P6249 4 GHz 5X Active Probe Instruction Manual

The probe head assembly contains an active amplifier circuit that
buffers and amplifies the input signal. The amplifier receives power
and an offset level from the compensation box assembly via the
cable assembly.

All signal amplification and buffering is performed in the probe head
assembly. No further amplification takes place in the compensation
box.

The compensation box contains the following circuits:

H Offset amplifier
H Probe identification EEPROM
H TEKPROBE interface
H V

CC

, +7 V linear regulator

The offset amplifier is used to offset the input signal DC component
so that it stays at the optimal point of the probe linear dynamic
range. For more information on the linear dynamic range characteris-
tic, refer to Input Linear Dynamic Range on page 19.

The offset amplifier receives offset information as a 

±1 VDC voltage

from the oscilloscope. The amplfier then amplifies it to match the
probe characteristics and applies it to the probe head circuit.

The offset amplifier has two adjustments: offset zero and offset gain.
These adjustments rarely need attention; however, detailed
adjustment instructions are in the Adjustment section on page 49.

The probe identification EEPROM is used to configure the
oscilloscope to the probe. The EEPROM receives a clock input from