• • Mean = 80
Standard Devia=on = 14 66 80 94
• • • • • Midterm 1 15% (10-‐14-‐11) Midterm 2 15% (11-‐4-‐11) Final Exam 30% (12-‐8-‐11 noon-‐ 3 pm) Homework 20% (Homework 4 due Monday) Quizzes 20% (lowest quiz grade dropped, quiz 3 on Monday)
If you are not going to be able to take the midterms and the ﬁnal exam on these dates you should take this class at a later date!
So What’s So Good About Feedback? • • With lots of feedback the feedback network determines the gain and the gain of the ampliﬁer is not important – Passive components are rela=vely stable – Ac=ve components are less stable – they dri] & are more sensi=ve to the environment (temp, etc. Impact of noise is reduced (see next slide).
So What’s So Good About Feedback? Reference: Intersil Ap Note on Feedback, Op Amps and Compensa=on (posted on EE 101 website under “Reference Documents.”)
Summing Ampliﬁer • Summing Ampliﬁer is an op amp circuit that combines several inputs and produces an output that is the weighted sum of the inputs. 6
Summing Ampliﬁer Example Calculate
in the op amp mixer circuit shown below. 7
Diﬀeren=al Ampliﬁer with Op Amp • Diﬀerence ampliﬁer is a device that ampliﬁes the diﬀerence between two inputs but rejects any signals common to the two inputs (common mode interference) . Analysis: Apply KCL at both nodes a & b and solve for v o . Reject common mode 8
Common Mode Interference • • • Common mode is applied to both inputs, e.g. between a cable shield and two internal wires. Diﬀeren=al amp rejects common mode signals. Check Op Amp spec sheet for CMRR = A D /A CM
Common ~ Gnd Diﬀeren=al ~ - +
5.4 Cascaded Op Amp (1) • It is a head-‐to-‐tail arrangement of two or more op amp circuits such that the output to one is the input of the next.
v o v
3 10 €
• Find v – o and i o in the circuit shown below Recognize cascaded, non-‐inver=ng amps (signal applied to non-‐ inver=ng input) – – Determine gain of each stage and use cascaded gain to ﬁnd v o Use knowledge of va and vb and then Ohm’s Law across 10 k Ω resistor Ans: 350mV, 25μA 11
5.4 Cascaded Op Amp (3) If v 1 = 1V and v 2 = 2V, ﬁnd v o in the op amp circuit shown below. Ans: 8 2/3 V 12
DAC Applica=on • Digital-‐to Analog Converter (DAC) : it is a device which transforms digital signals into analog form. Four-‐bit DCA: (a) block diagram (b) binary weighted ladder type Summing Ampliﬁer where V 1 – MSB, V 4 – LSB V 1 to V 4 are either 0 or 1 V 13
DAC Circuit Example For the circuit shown below, calculate v o if v 1 = 0V, v 2 =1V and v 3 = 1V. Ans:-‐0.75V 14