Download presentation

Presentation is loading. Please wait.

1
**Differential Amplifiers**

2
Outline

3
**Single-Ended Versus Differential Operation**

The transitions disturb the differential by equal amounts, leaving the difference in tact.

4
**Immunity to Supply Noise**

If VDD changes by ∆V, Vout changes by the same amount. Noise in VDD affects VX and VY, but not Vx-Vy

5
**Reduction of Coupled Noise**

Noise coupled from L3 to L1 and L2 to L1 cancel each other.

6
**Sensitivity to the Common mode level**

Excessive low Vin,CM turns off Devices.

7
**Basic Differential Pair**

8
**Schematic of Differential Amplifier**

9
**Input/Output Characteristics**

Minimum Slope Independent of Vin,cm Maximum Slope Thus maximum Gain

10
**Range of Vin,cm Lower bound of Vin,cm:**

VP should be sufficiently high in order for M3 to act as a current source. Upper bound of Vin, cm M1 and M2 need to remain in saturation.

11
**Sensitivity to Vin, cm M3 in the linear region is modeled**

as a resistor M1=M2 =On M1=M2 =Off M1=M2 =On M1=M2 =Off M1=M2 =On M1=M2 =Off M3=Linear M3=Linear M3=Linear

12
**Small signal Gain as a function of Vin, CM**

13
**Maximum Allowable Output Swing**

The higher the input CM level, the smaller the allowable output swings.

14
Transconductance ∆Vin1Represents the maximum differential signal a differential pair can handle.

15
Linearity W/L increases ISS Constant Constant W/L ISS increases

16
**Determinations of Small Signal Gain**

CS with resistive source degeneration Thevenin Resistance Cascode Superposition Principle

17
**CS with resistive source degeneration**

Interpretation: The resistance at the drain Divided by the resistance in the source path

18
**Treat M1 as a CS stage with resistive source degeneration to find VX/Vin**

19
**Replace M1 by its Thevenin Equivalent Circuit**

If RS is sufficiently large, then the small signal gain of the amplifier can be obtained using thevenin’s equivalent circuit (see hand out)

20
Gain of CG

21
**Replace M1 by its Thevenin Equivalent Circuit**

22
Small Signal Gain

23
Half-Circuit Concept

24
**Conversion of Arbitrary inputs to Differential and Common-Mode Components**

25
**Superposition Principle**

26
**Schematic of Differential Amplifier**

27
Simulation Vin,m=1 mV Vout,m=8.735 mV Av=-8.735 Calculations: Gm=1mS ro=30.53 KOhm RL=12 Kohm Av=-Gm(ro||RL)=-8.615

28
**Common-Mode Response Sensitivity of Vout,CM due to Vin,CM**

In the presence of resistor mismatch In the presence of transistor mismatch Common Mood Rejection Ratio (CMRR)

29
**Sensitivity of Vout,CM due to Vin,CM**

Vin,CM ↑, VP ↑, I(RSS) ↑,VX,V↓

30
**Output CM Sensitivity due to Vin, CM**

Vout,m =0.285 mV Vin,cm =1 mV RL=12 K Gm=1.043 mS Gds3=58.29 uS Av, CM(Analytical)=0.343 Av, CM(Simulation)=0.285 (Excluding gmb, ro)

31
**Common-Mode to Differential Conversion at High Frequencies**

Even if the output resistance of the current source is high, the common-mode to differential conversion becomes significant at high frequencies.

32
Resistor Mismatch (from CS with resistive source degeneration)

33
**Common Mode to Differential Mode Conversion**

34
Voutp-Voutn Differential Mode signal at the output: uV

35
**Effect of CM Noise in the Presence of Resistor Mismatch**

Common Mode to Differential Conversion

36
Transistor Mismatch

37
**Supply Noise Sensitivity**

38
CMRR

39
Diode Connected Load Problem: Difficult to decrease (W/L)P without dropping the common mode voltage of Vout.

40
**Addition of Current Source to Increase Voltage Gain**

Reduce gm by reducing current rather than the aspect ratio. Reduce I(M3) and I(M4).

41
**Variable Gain Amplifier**

Similar presentations

Presentation is loading. Please wait....

OK

Differential Amplifiers

Differential Amplifiers

© 2018 SlidePlayer.com Inc.

All rights reserved.

To make this website work, we log user data and share it with processors. To use this website, you must agree to our Privacy Policy, including cookie policy.

Ads by Google