A 92MHz, 80dB peak SNR SC bandpass ΣΔ modulator based on a high GBW OTA with no Miller capacitors in 0.35μm CMOS technology

Author

Thandri, Bharath Kumar ; Martinez, Jose Silva ; Rocha-Perez, Jose Miguel ; Wang, Jing

Author_Institution

Dept. of Electr. Eng., Texas A&M Univ., College Station, TX, USA

fYear

2003

fDate

21-24 Sept. 2003

Firstpage

123

Lastpage

126

Abstract

An OTA with a feedforward compensation scheme uses positive phase shift of left half plane (LHP) zeros created by a feedforward path to cancel the negative phase shift of poles, thereby overcoming the limitations of traditional Miller compensation schemes. The OTA is used in the design of a fourth order switched capacitor bandpass ΣΔ modulator with the IF at one-fourth of the sampling frequency. The modulator uses a cascade of resonators in a feedback architecture, along with feedforward paths for stability. Experimental results for the bandpass modulator designed in TSMC 0.35 μm CMOS technology show a peak SNR of 80 dB and 54 dB for 270 kHz and 3.84 MHz bandwidth at 92 MHz clock and consumes 19 mA from a ±1.25 V supply. The OTA has a DC gain of 80 dB, 1.4 GHz GBW, phase margin of 62° and 2 ns settling time for 2 pF load capacitor.

Keywords

CMOS integrated circuits; circuit feedback; circuit stability; feedforward; integrated circuit design; operational amplifiers; poles and zeros; resonators; sigma-delta modulation; switched capacitor networks; 0.35 micron; 19 mA; 2 ns; 2 pF; 2.5 V; 270 kHz; 3.84 MHz; 80 dB; 92 MHz; CMOS technology; LHP positive phase shift; Miller compensation schemes; SC modulator; SNR; bandpass ΣΔ modulator; feedback; feedforward compensation scheme; high GBW OTA; phase margin; poles; resonator cascade; sampling frequency; settling time; stability; switched capacitor modulator; zeros; Bandwidth; CMOS technology; Capacitors; Clocks; Feedback; Filtering theory; Frequency modulation; Poles and zeros; Sampling methods; Stability;

fLanguage

English

Publisher

ieee

Conference_Titel

Custom Integrated Circuits Conference, 2003. Proceedings of the IEEE 2003

Print_ISBN

0-7803-7842-3

Type

conf

DOI

10.1109/CICC.2003.1249374

Filename

1249374