The document discusses various concepts related to analog electronics, focusing on precision amplifiers, log amplifiers, antilog amplifiers, and multiplier circuits. It outlines the principles and applications of circuits like sample and hold, track and hold, and four quadrant multipliers. Additionally, it mentions practical applications in modulation, analog computation, and filtering technologies.

2. Analog Electronics (ECE F341/EEE F341/ INSTR F341 )
Lecture 12
(Precision amplifier)
Instructor
Dr. Apurba Chakraborty
Assistant Professor
Department of Electrical and Electronics Engineering
BITS Pilani, K K Birla Goa Campus
Date: 6/2/2024

3. Log Amplifier
• 𝐼𝐶 = 𝐼𝑖 =
𝑉𝑖
𝑅1
= 𝐼𝑆(𝑒
𝑉𝐵𝐸
𝑉𝑇 − 1)
•
𝑉𝑖
𝑅1
= 𝐼𝑆 𝑒
𝑉𝐵𝐸
𝑉𝑇 --------------(1)
We can write
• 𝑉𝐵𝐸 + 𝑉0 = 0 => 𝑉𝐵𝐸 = −𝑉0
From eq 1,
• 𝑽𝟎 = −
𝒌𝑻
𝒒
𝐥𝐧(
𝑽𝒊
𝑰𝒔𝑹𝟏
)
Diode can also be used for this
design

4. Antilog amplifier
𝑉𝑖𝑛 = −𝑉𝐵𝐸 -------------------(1)
𝐼𝑖 = 𝐼𝑆 𝑒
𝑉𝐵𝐸
𝑉𝑇 − 1 = 𝐼𝑆 𝑒
−𝑉𝑖𝑛
𝑉𝑇 =
𝑉0
𝑅𝐹
=> 𝑽𝟎 = 𝑹𝑭𝑰𝑺𝐞𝐱𝐩
−𝒒𝑽𝒊
𝒌𝑻
= 𝑹𝑭𝑰𝑺 (antilog(
−𝒒𝑽𝒊
𝒌𝑻
)

5. Multiplier circuit:

6. Division circuit:
𝑉𝑍 = −𝑉1 --------(1)
𝑉1= K𝑉𝑋𝑉0 = −𝑉𝑍
𝑽𝟎 =
−𝑽𝒁
𝑲𝑽𝑿

7. Square root circuit:
𝑉𝑍 − 0 = 0 − 𝑉1 --------(1)
𝑉1= K𝑉0𝑉0 = −𝑉𝑍
if the magnitude is negative
𝑉0= 𝑉𝑍 /𝐾
So the input no must be negative.

8. Amplitude modulation

9. (
𝑉𝑚𝐸𝑐𝐶𝑜𝑠 ω𝑡
𝐾
− 𝑉𝑋)𝑚𝐾 = 𝑉𝑋- 𝐸𝑐𝐶𝑜𝑠 ω𝑡
=> 𝑚𝑉
𝑚𝐸𝑐𝐶𝑜𝑠 ω𝑡 + 𝐸𝑐𝐶𝑜𝑠 ω𝑡 = 𝑉𝑋+𝑉𝑋mK-----------(1)
we can write
𝑉
𝑜 = 1 + 𝑚𝐾 𝑉𝑋
= 𝑚𝑉
𝑚𝐸𝑐𝐶𝑜𝑠 ω𝑡 + 𝐸𝑐𝐶𝑜𝑠 ω𝑡 from eq 1.
This is AM signal.

10. Sample and hold circuit:
• This circuit samples the input signal and holds the last value of input. The value of the signal will remain
same until the next data is sampled.
• Useful in A to D converter and Pulse width modulation.

12. Track and Hold circuit
In Sample and hold circuit, the input voltage is captured
instantaneously . But, in real the instantaneously capturing
of voltage is unfeasible due to inherent dynamic limitation
of physical circuits.

13. Track and Hold circuit

14. Switches

15. Use of Switch in Multiplexing

16. Four quadrant Multiplier:
This is the general multiplier circuit
characteristics.
It is called four quadrant Multiplier.

17. Multiplier design by Variable transcoductance amplifier
By proper design ,
K= 1/10 V
𝑉0 = 𝑉𝑍1 − 𝑉𝑍2
𝑉𝑋 = 𝑉𝑋1 − 𝑉𝑋2
𝑉𝑌 = 𝑉𝑌1 − 𝑉𝑌2
Variety of monolithic multiplier
like
AD534 and MPY 100.

18. Applications:
• Modulation and demodulation
• Analog computation
• Phase detection etc.
At low pass filter, all high frequency components are suppressed
This circuit can be a phase detector or ac power computation circuit.

19. Four quadrant Divider
Four quadrant square root