70009 Parallax Inc, 70009 Datasheet - Page 112

• Manufacturer Part Number: 70009
• Description: BOOK UNDERSTANDING SIGNALS
• Manufacturer: Parallax Inc
• Type: Signal Analysisr

Specifications of 70009

• Style: Book
• Title: Understanding Signals
• Contents: Guide to Generate, View and Measure Wave Forms
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Other names: 70009PAR

Therefore, a 20 kΩ resistor is needed for Rf, given a 10 kΩ resistor for Ri and a desired
gain of 2. Remember, the 10 kΩ resistor in the input impedance of the op-amp.
Two 10 kΩ resistors would present themselves as an additional load (Figure 8-6). The
two 10 kΩ resistors when measured at the middle should yield 2.5 V. When you connect
your op-amp circuit to a 2.5 V signal, you might see something less than 2.5 V. The
output impedance of the resistor divider is high, meaning it does not supply very much
current. The inverting op-amp circuit has low input impedance, hence the 10 kΩ input
resistor. So, the op-amp circuit will load down the 2.5 V signal, causing it to sag.
When using inverting op-amp circuits, keep what you have just learned in mind. You can
increase the value of Ri in the op-amp circuit to increase the input impedance, but if you
can, keep the value around 10 kΩ.
A non-inverting voltage amplifier has its input signal applied directly to the non-inverting
input of the op-amp (Figure 8-7). This gives you very high input impedance, up to 2 MΩ
Vss
Vss
+5
Signal
Ri
Vss
Vss
OPAMP 10 k Input
approximation
impedance
Rf
Vss
Vout
Figure 8-6:
Two 10k resistors
have significant
output impedance.
Figure 8-7:
Non-inverting
Voltage Amplifier