ECE201 Lect-181 RC Op-Amp Circuits (6.4) Dr. Holbert April 10, 2006

ECE201 Lect-182 Digital Meters and Oscilloscopes Most multimeters and oscilloscopes are now digital. A digital multimeter or a digital oscilloscope has an analog-to-digital (A/D) converter. Most digital meters and all digital oscilloscopes have one or more processors.

ECE201 Lect-183 Data Acquisition Systems In many applications, digital meters and scopes are being replaced by data acquisition cards that fit into a computer. The data acquisition cards have A/D converters. The computer provides processing and storage for the data.

ECE201 Lect-184 A Generic Digital Meter Input Switching and Ranging Amplifier A/D Converter ProcessorDisplay

ECE201 Lect-185 Voltage Measurements HiCom 10V 1V 100V

ECE201 Lect-186 Model for Meter The ideal meter measures the voltage across its inputs. No current flows into it; it has infinite input resistance. 10M  Ideal Meter Hi Com

ECE201 Lect M  Ideal Meter Hi Com R Meter Loading The 10M  meter resistance in parallel with R may change the voltage that you measure.

ECE201 Lect-188 Loading When measuring the voltage across R, we need to make sure that R is much less than 10M  If R is close to 10M , significant current flows through the meter, changing the voltage across R.

ECE201 Lect-189 Loading Example Without Meter: voltage is 100V With Meter: measured voltage is 83.3V 10M  Ideal Meter Hi Com 2M  50  A

ECE201 Lect-1810 Current Measurements AmpCom 10V 1V 100V

ECE201 Lect-1811 Measuring Large Currents (> 100mA) The current to be measured is passed through a small resistor (called a shunt resistor) and the resulting voltage across the shunt resistor is measured. From the voltage, the current can be computed.

ECE201 Lect-1812 RsRs Ideal Meter Amp Com R Meter Loading The R s shunt resistance in series with R may change the current that you measure.

ECE201 Lect-1813 The Voltage Follower v in + – v out + – +–+–

ECE201 Lect-1814 Without a Voltage Follower v A/D is not equal to v s vsvs RsRs R A/D + – v A/D Sensor A/D Converter +–+–

ECE201 Lect-1815 Op-Amp Review The ideal op-amp model leads to the following conditions: i + = i - = 0 v + = v - The op amp will set the output voltage to whatever value results in the same voltages at the inputs.

ECE201 Lect-1816 Op-Amp Review To solve an op-amp circuit, we usually apply KCL (nodal analysis) at one or both of the inputs. We then invoke the consequences of the ideal model. We solve for the op-amp output voltage.

ECE201 Lect-1817 With a Voltage Follower v A/D is equal to v s vsvs RsRs Sensor R A/D + – v A/D A/D Converter + – +–+–

ECE201 Lect-1818 An Integrator – + V in + – V out R C +–+–

ECE201 Lect-1819 KCL at the Inverting Input – + v in (t) + – R C v out (t) iR(t)iR(t) iC(t)iC(t) i-i- +–+–

ECE201 Lect-1820 KCL

ECE201 Lect-1821 Solve for v out (t)

ECE201 Lect-1822 Class Example Learning Extension E6.9