TF EIMLab23 Writeup - Revision history

Foretony: /* I_{io} */

2011-04-20T18:24:15Z

I_{io}

2011-04-20T18:23:45Z

V_{io} and I_{B}

2011-04-20T01:58:57Z

Inverting OP Amp

2011-04-20T01:58:30Z

Inverting OP Amp

2011-04-19T03:29:48Z

Input Impedance

2011-04-19T03:28:55Z

Input Impedance

2011-04-19T02:56:24Z

Output Impedance

2011-04-19T02:49:30Z

Input Impedance

2011-04-19T02:44:58Z

The offset Null Circuit

2011-04-19T02:44:14Z

Gain measurements

@@ Line 80: / Line 80: @@
 Instead of the current <math>I_B</math> we have the current <math>I_{io}</math>
-;<math>V_{out}= -\frac{R_1}{R_2} V_1 + \left ( 1 + \frac{R_1}{R_2}\right)V_{io}  + R_2 I_{io}</math>
+;<math>V_{out}= -\frac{R_2}{R_1} V_1 + \left ( 1 + \frac{R_2}{R_1}\right)V_{io}  + R_2 I_{io}</math>
 Use the same technique and resistors from the previous section to construct 2 equations and 2 unknowns and extract <math>I_{io}</math>, keep <math>V_{in}</math>=0.

@@ Line 64: / Line 64: @@
 = <math>V_{io}</math> and <math>I_{B}</math>=
-;<math>V_{out}= -\frac{R_1}{R_2} V_1 + \left ( 1 + \frac{R_1}{R_2}\right)V_{io}  + R_2 I_B</math>
+;<math>V_{out}= -\frac{R_2}{R_1} V_1 + \left ( 1 + \frac{R_2}{R_1}\right)V_{io}  + R_2 I_B</math>
 Use the above equation and two measurements of <math>V_{out}</math>, <math>R_1</math>, and <math>R_2</math>  to extract <math>V_{io}</math> and <math>I_B</math>.

← Older revision		Revision as of 01:58, 20 April 2011
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−	[[File:TF_EIM_Lab23WriteUp_741Pinouts.png]]	+	[[File:TF_EIM_Lab23WriteUp_741Pinouts.png\| 200 px]]

	Use <math>R_1 = 1k\Omega</math> and <math>R_2 = 10 k\Omega</math> as starting values.		Use <math>R_1 = 1k\Omega</math> and <math>R_2 = 10 k\Omega</math> as starting values.

← Older revision		Revision as of 01:58, 20 April 2011
Line 9:		Line 9:
	[[File:LM741CN_OpAmp.pdf]]		[[File:LM741CN_OpAmp.pdf]]

		+
		+	[[File:TF_EIM_Lab23WriteUp_741Pinouts.png]]

	Use <math>R_1 = 1k\Omega</math> and <math>R_2 = 10 k\Omega</math> as starting values.		Use <math>R_1 = 1k\Omega</math> and <math>R_2 = 10 k\Omega</math> as starting values.

@@ Line 35: / Line 35: @@
 {| border="3"  cellpadding="20" cellspacing="0"
-|V_{in} (V)|| I_{in} A|| \frac{V_{in}}{I_{in}}
+|<math>V_{in} </math>(V)|| <math>I_{in} </math>(A)||<math> \frac{V_{in}}{I_{in}} \Omega</math>
 |-
 |  || ||

← Older revision		Revision as of 03:28, 19 April 2011
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	There is a tiny input bias current for an op-amp which is about 80 nA for 741 type op-amps.		There is a tiny input bias current for an op-amp which is about 80 nA for 741 type op-amps.
		+
		+
		+	{\| border="3" cellpadding="20" cellspacing="0"
		+	\|V_{in} (V)\|\| I_{in} A\|\| \frac{V_{in}}{I_{in}}
		+	\|-
		+	\| \|\| \|\|
		+	\|-
		+	\| \|\| \|\|
		+	\|-
		+	\| \|\| \|\|
		+	\|-
		+	\| \|\| \|\|
		+	\|-
		+	\| \|\| \|\|
		+	\|}

	==Output Impedance==		==Output Impedance==

← Older revision		Revision as of 02:56, 19 April 2011
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	==Output Impedance==		==Output Impedance==
	#Measure <math>R_{out}</math> for the 10 fold and 100 fold amplifier at ~100 Hz and 10 kHz frequency. Be sure to keep the output (<math>V_{out}</math>) undistorted		#Measure <math>R_{out}</math> for the 10 fold and 100 fold amplifier at ~100 Hz and 10 kHz frequency. Be sure to keep the output (<math>V_{out}</math>) undistorted
		+
		+
		+	To show that the output impedance is small, observe the gain at f = 1 kH z with an
		+	output load of 10 Ω. Note that the maximum output current of the 411 is about 20 mA,
		+	so limit the output voltage to less than 200 mV .
		+

← Older revision		Revision as of 02:49, 19 April 2011
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	For the 741 the input resistance measured to one input with the other grounded is about 2 Megohms.		For the 741 the input resistance measured to one input with the other grounded is about 2 Megohms.
		+
		+
		+	There is a tiny input bias current for an op-amp which is about 80 nA for 741 type op-amps.

	==Output Impedance==		==Output Impedance==

@@ Line 65: / Line 65: @@
 #Adjust the potentiometer  to minimize <math>V_{out}</math> with <math>V_{in}=0</math>.
 #Use a scope to measure the output noise.
 = Capacitors=

← Older revision		Revision as of 02:44, 19 April 2011
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	2.)Graph the above measurements with the Gain in units of decibels (dB) and with a logarithmic scale for the frequency axis.		2.)Graph the above measurements with the Gain in units of decibels (dB) and with a logarithmic scale for the frequency axis.
		+
		+
		+	One of the practical op-amp limitations is that the open loop gain which is so high at frequencies in the kHz range (100,000 to a million or more) drops to a gain of one at some high frequency (say 1 to 10 MHz). Many op-amps contain internal compensation to cause a 6dB per octave rolloff of gain (like a low-pass filter) at some chosen frequency to stabilize the unit against high frequency oscillations. For the 741 this rolloff starts at 100 kHz. From the beginning of the rolloff the RC type filter action leads to phase shift starting at 90¡ and increasing to 120¡ to 160¡ as the gain approaches one. If the phase shift reaches 180¡ the feedback becomes positive and the system can oscillate.

	=Impedance=		=Impedance=