Theory of Operation
36 P6249 4 GHz 5X Active Probe Instruction Manual
Probe Head and Cable Assembly
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.
Compensation Box
The compensation box contains the following circuits:
HOffset amplifier
HProbe identification EEPROM
HTEKPROBE interface
HVCC, +7 V linear regulator
Offset Amplifier
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.
Probe Identification EEPROM
The probe identification EEPROM is used to configure the
oscilloscope to the probe. The EEPROM receives a clock input from