Download presentation

1
**Linearized MOSFET Resistors**

Dr. Paul Hasler

2
Review of Gm-C Filters Gm-C filters: voltage mode/current mode/log-domain Use amplifier dynamics as filtering elements: If making 10kHz filter, why make amplifiers run at 10MHz? Good properties Highest bandwidth / power consumed Smallest number of elements / area consumed Lowest noise levels / power consumed (thermal) Utilizes capacitor matching (ie. C4) Electronically tunable

3
**Issues for Gm-C Filters**

Improvement by Floating-Gate Techniques Tuning Need control schemes (direct or indirect) – adds significant amount of control overhead Mostly compensates: slight adjustments due to transistor aging / T changes, etc. Matching Huge issue for current-mode techniques Design to eliminate these issues Distortion Techniques to improve linear range, but at a cost of lower gm/I (lower speed, higher noise, higher power) More techniques to improve linear range Most Gm-C techniques are fairly recent (80’s-90’s), and Floating-Gate techniques are even more recent (90’s - ).

4
**Other Filter Techniques**

Utilizing higher frequency elements / additional elements, to improve distortion (as well as 1/f noise, etc.). Two techniques: Amplifiers: (Op-amps), that run at much faster frequencies than filter cutoff. Can use feedback to widen the linear range. Significant power increase. Oversampling: Using a wider bandwidth than necessary to lower noise per unit bandwith (and more power) and distortion. Nonlinear systems can utilize noise shaping (Sigma-Delta Modulators) Common in sampled data systems. Switched Capacitor Blocks Blocks based upon traditional, discrete RC active fitlers.

5
**How to Build Resistances?**

Resistors in a CMOS process - Sometimes High resistance poly layer in a given process - Poly, diffusions, or Well, but larger area consumed Fairly linear, can be large for frequencies under 1MHz. Not tunable: therefore RC > 20% mismatch, so we have a problem for precission filters…so either laser trimming, EEPROM trimming, (could tune cap, but…) or imprecise filters, like anti-alaiasing filter. MOSFET as a Resistor

6
MOSFET as a Resistor Ohmic Region: how linear will that be, well only over a small region. We have a gate voltage, so it is tunable, but of course, we still need a method of tuning. MOSFET has an ohmic region both in subthreshold and above threshold operation. Resistance is not exactly a constant, except for a fixed source voltage…. resistance changes with source / drain voltage. Could imagine an nFET and a pFET in parallel, but still not a precission element.

7
**MOSFET as a Resistor Two things to improve the situation.**

1. Typically built around an amplifier to fix one of the terminals (mostly op-amps, but could also be a Norton or transisresistance approach as well) The amplifier must keep terminals nearly fixed to eliminate distrotion; therefore, in general the amplifier must run a lot faster than expected by a simple GmC stage. 2. Can use a combination of MOSFETs to linearize the behavior.

8
**Linearized MOSFET resistors**

Simple Structure Balanced Differential Element Vc + Va + Vc + - Va + Vi + Vi Iout + Iout + Iout - Vi Iout - Vi - Va - Vc - Va -

9
**Linearized MOSFET resistors**

In practice, one might use even lower input impedance elements Vc + - Vi + Iout + Iout - Vi - Iout - Va + Iout + Va - GND GND GND GND

10
**Basic Resistive Feedback**

Vc + Vi + GND Vout Vout + Vin Vc - Vc - R1 Vout - Vi - Vb + - R2 Vc +

11
**Basic Integrator Structure**

Vc + Vi + Vout + GND Vout Vin Vc - Vc - Vout - R1 Vi - C Vc + C Vb - Vb - Vb + Vb + Vb + Vb - Ideal Integrator if =

12
**Tow-Thomas SOS (Lowpass)**

C1 R3 C2 R R1 R4 R2 Vin R GND V1 Vout GND V2 GND R4 needed for stability Tuning can be interesting (tuning pots) All amps must be sufficiently fast

13
**Tow-Thomas SOS (Lowpass)**

C R C R R R4 R Vin R GND Vout GND GND t = RC Q = R4 / R

Similar presentations

OK

Week 6aEECS40, Spring 2005 Week 6a OUTLINE Op-Amp circuits continued: examples Inverting amplifier circuit Summing amplifier circuit Non-inverting amplifier.

Week 6aEECS40, Spring 2005 Week 6a OUTLINE Op-Amp circuits continued: examples Inverting amplifier circuit Summing amplifier circuit Non-inverting amplifier.

© 2018 SlidePlayer.com Inc.

All rights reserved.

To ensure the functioning of the site, we use **cookies**. We share information about your activities on the site with our partners and Google partners: social networks and companies engaged in advertising and web analytics. For more information, see the Privacy Policy and Google Privacy & Terms.
Your consent to our cookies if you continue to use this website.

Ads by Google

Ppt on 3 r's of environment Ppt on plain cement concrete Ppt on stock markets in india Ppt on forest society and colonialism free download Ppt on combination of resistances organization Ppt on acid base and salts Ppt on covering the environmental problems causes effects and solutions Upload and view ppt online reader Ppt on online advertising in india Ppt on network theory