Agilent Technologies 34970A, Руководство пользователя, Страница: 316 / 356

316
Chapter 7 Tutorial
Multifunction Module
Using an External Pull-Up
In general, an external pull-up is required only when you want to set the
output “high” value greater than TTL levels. For example, to use a +12V
external power supply, the value of the external pull-up resistor is
calculated as follows:
VDC
I
max
= I
out low
x safety factor = 1 mA x 0.5 + 0.5 ma
= 24 k 
The value of the logic “high” level with the external 24 k  pull-up
resistor is calculated as follows:
V
high
= V
cc
x = 12 x = 8.47 VDC
Driving External Switches
You can use two digital output channels to control an external switch.
For example, you can drive the Agilent 876X series of microwave
switches using an external power supply and two digital output
channels. The state of the 2-to-1 multiplexer is changed by setting the
appropriate output bit low (0).
V
cc
12 =
R
V
cc
I
max
-----------
12
0.0005
·
------------------ = =
R
external
R
external
R
externa l
+
-------------------------------------------------------
24 k 
24 k  10 k  +
----------------------------------------
Digital Output Channel Agilent 876X Microwave Switch
Power
24 Volt
Supply
34970A Refresh UG.book Page 316 Wednesday, February 17, 2010 12:34 PM