Motivation. Many applications require a front end opamp that is capable of providing both a fast and accurate response:These include A/D convertors, Switched capacitor filters, Sample-and-hold amplifiersUnfortunately, there is typically a tradeoff between speed and accuracy. Circuit Requirements
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1. A 90dB High Bandwidth Single Stage Amplifier Arthi Ramamurthy
2. Motivation Many applications require a front end opamp that is capable of providing both a fast and accurate response:
These include A/D convertors, Switched capacitor filters, Sample-and-hold amplifiers
Unfortunately, there is typically a tradeoff between speed and accuracy
3. Circuit Requirements These applications need an opamp with :
High DC gain (accuracy)
Low current levels with long channel devices
High Unity gain (speed)
Single-pole settling (-20 db/decade)
High current level in short channel devices
A regulated cascode overcomes this conflict
4. Regulated Cascode Rout of each cascode is increased by A (HW#4)
Additional amplifiers should have high gain but can be slow
5. Frequency Response of Regulated Cascode High frequency response unchanged
DC gain is boosted considerably
Unity gain frequency unchanged (output pole still dominant)
6. Our implementation Gain boost amplifiers were implemented as folded cascode amplifiers
Common mode feedback was used to control the output level of the circuit
Biasing circuits were created to control the opamps
Additional stages are very small (10-20% increase in total die area)
7. Regulated Cascode
9. Evaluating the design
10. Range of Operation Vdd: 2.5 ? 5%
If conditions above are followed:
Voltage Swing > 750 mV
Phase Margin > 59
Unity Gain Frequency > 100 MHz
11. Summary of Operating Conditions
12. Conclusion Gain boosting is effective for increasing the gain of a single stage amplifier
Using this technique we were able to achieve 90dB gain and 275Mhz unity gain while driving a 2pF load
13. References Bult, K. Geelen, G.J.G.M; A fast-settling CMOS op amp for SC circuits with 90-dB DC gain. IEEE Journal of Solid-State Circuits, Volume: 25 Issue: 6 , Dec. 1990, p. 1379 -1384.
Burger, T.; Qiuting Huang; A 100 dB, 480 MHz OTA in 0.7 Ám CMOS for Sampled-Data Applications. Custom Integrated Circuits Conference, 1996., Proceedings of the IEEE 1996, p. 101-104.
Burger, T.; Qiuting Huang; On the Optiumum Design of Regulated Cascode Operational Transconductance Amplifiers. International Symposium on Low Power Electronics and Design.,1998, p. 203-208.
Gulati; K; A ▒2.45 V-swing CMOS telescopic operational amplifier. IEEE Journal of Solid-State Circuits, Volume: 33 Issue: 12, Dec. 1998, p. 2010 -2019.
14. Folded Cascode