HighZ Attenuator

The first section of attenuator switch S105A directs the input signal to one of three paths: directly through R103 (no attenuation); through a 10X attenuator consisting of C105, C107, R105, R106, R107, and R108; or through a 100X attenuator consisting of C111, C112, R110, R111, R112, R114, and R115. Medium-frequency normalization of the input capacitance is accomplished by

Figure 3-2. Detailed block diagram of the Channel 1 attenuator and attenuator switching tables.

S101

AC-GND-DC

^R101

INPUT COUPLING

S105 -- VOLTS/DIV

CH 1

INPUT

BUFFER

AMPLIFIER

U120

Q122

Q125,

Q133

Q134,

Q139

CAL

1

VOLTS/ DIV VAR

LOW-Z ATTENUATOR -5- 1 > + 2.5, + 5

X1/X10 AMPL UM5

HIGH-Z ATTENUATOR

LOW-Z ATTENUATOR

X1/X10 AMPL

HIGH-Z ATTENUATOR

LOW-Z ATTENUATOR

VOLTS/ DIV

+ 1

4-10

+ 100

VOLTS/ DIV

+ 1

+ 2.5

+ 5

2 mV

X

2 mV

X

5 mV

X

5 mV

X

10 mV

X

10 mV

X

20 mV

X

20 mV

X

50 mV

X

50 mV

X

100 mV

X

100 mV

X

200 mV

X

200 mV

X

500 mV

X

500 mV

X

1 V

X

1 V

X

2 V

X

2 V

X

5 V

X

5 V

X

10 V

X

10 V

VOLTS/ DIV

X1

X10

2 mV

X

5 mV

X

10 mV

X

20 mV

X

50 mV

X

100 mV

X

200 mV

X

500 mV

X

1 V

X

2 V

X

5 V

X

10 V

X

C104 in the 10X attenuator and by C110 in the 100X attenuator. Switch S105B connects the appropriate attenuator output to the input of the Buffer Amplifier.

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