High-performance, high-frequency operational transconductance amplifiers (OTAs) are very important elements in the design of high-frequency continuous-time integrated analog signal processing circuits, because resistors, inductors, integrators, mutators, buffers, multipliers, and filters can be built by OTAs and capacitors. The critical considerations for OTA design are linearity, tuning, frequency response, output impedance, power supply rejection (PSR) and common-mode rejection (CMR). For linearity considerations, two different methods are proposed. One uses cross-coupled pairs (CMOS or NMOS), producing OTAs with very high linearity but either the input range is relatively small or the CMR to asymmetrical inputs is poor. Another employs multiple differential pairs (current addition or subtraction), producing OTAs with high linearity over a very large input range. So, there are tradeoffs among the critical considerations. For different applications, different OTAs should be selected. For consideration of frequency response, the first reported GaAs OTA was designed for achieving very-high-frequency performance, instead of using AC compensation techniques. GaAs is one of the fastest available technologies, but it was new and less mature than silicon when we started the design in 1989. So, there were several issues, such as low output impedance, no P-channel devices, and Schottky clamp. To overcome these problems, new techniques are proposed, and the designed OTA has comparable performance to a CMOS OTA. For PSR and CMR considerations, a fully balanced circuit structure is employed with a common-mode feedback (CMF) circuit used to stabilize the DC output voltages. To reduce the interaction of the operation of CMF and tuning of OTAs, three improved versions of the CMF circuits used in operational amplifiers are proposed. With the designed OTAs, a I GHz GaAs inductor with small parasitics is designed using the proposed procedure to reduce high-frequency effects. Two CMOS high-order, high-frequency filters are designed: one in cascade structure and one in LC ladder form. Also, a 200 MHz third-order elliptic GaAs filter is designed with special consideration of very-high-frequency parasitics. All circuits were fabricated and measured. The experimental results were used to verify the designs.
| Identifer | oai:union.ndltd.org:pdx.edu/oai:pdxscholar.library.pdx.edu:open_access_etds-2161 |
| Date | 01 January 1993 |
| Creators | Wu, Pan |
| Publisher | PDXScholar |
| Source Sets | Portland State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Dissertations and Theses |
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