Ali Motamed

A low-voltage low-power wide-range CMOS variable gain amplifier

In this paper, a compact low-power (LP) low-voltage (LV) metal-oxide-semiconductor-only (MOS-only) variable gain amplifier (VCA) is introduced. This amplifier based on complementary MOS (CMOS) transistors operating in strong inversion is composed of a pseudo-exponential current-to-voltage converter, analog multiplier, and output stage. The gain of the amplifier is controlled exponentially by a novel wide-range pseudo-exponential current-to-voltage converter implemented with two back-to-back connected current mirrors exhibiting superb exponential characteristic. Also, a new LV/LP composite transistor is introduced to increase the input dynamic range of the multiplier. The amplifier is fabricated using a 2-/spl mu/m MOSIS n-well process, and its simulation and measurement results are shown in detail.

Universal constant-g/sub m/ input-stage architectures for low-voltage op amps

In this paper, a novel design technique for low-voltage, constant transconductance (g/sub m/) op amp input stages is presented. The new technique which uses current-mode circuits is based on processing signal currents, rather than handling DC tail currents, to achieve a constant-g/sub m/. Two cases are developed. One is based on processing signal currents (the AC case) while the other is based on processing total instantaneous currents (the TIC case). The adopted design strategy in both cases is universal in that it is independent of the input stage transistor types (FET or bipolar) and their operating regions. It also considerably simplifies the design procedure of low-voltage op amps. To demonstrate the new concepts, universal op amp input stage architectures have been developed and their performances have been verified in both MOS and bipolar design examples. The MOS designs have been verified in both weak and strong inversion. The proposed universal implementations achieve almost constant-g/sub m/, independent of the common mode input voltage range from rail-to-rail.

LV opamp with programmable rail-to-rail constant-g/sub m/

In this paper a new differential pair architecture with programmable rail-to-rail constant-g/sub m/ is presented and incorporated into an opamp. Since the architecture adopts a signal processing method to obtain constant-g/sub m/, it can be implemented in any complementary VLSI technology and it functions regardless of transistor operating regions. The experimental results of the proposed opamp show that the total transconductance is constant at any common mode input voltage (CMR) and programmed over very wide range simply by varying the bias current of the opamp. It is also shown that constant unity gain frequency and open loop gain are obtained at any CMR and total harmonic distortion is effectively reduced due to the constant-g/sub m/.

A simple universal LV/LP opamp architecture

In this paper a simple opamp input stage architecture with programmable rail-to-rail constant-g/sub m/ is presented. The constant-g/sub m/ is achieved by processing signal, rather than DC, currents. As a result, the architecture is universal in that it can be implemented in any complementary VLSI technology and it functions regardless of transistors operating region. A MOS implementation is discussed and is shown to operate in both weak and strong inversion, resulting in a programmable g/sub m/, or unity gain frequency, over a very wide range.

A programmable low-voltage micropower CMOS input stage architecture

A very simple CMOS rail-to-rail, constant-g/sub m/ opamp input stage architecture is presented. The constant-g/sub m/ is achieved by processing signal currents rather than DC bias currents. As a result, the architecture is universal in that it operates in both weak and strong inversion regions with small variations in g/sub m/.

Theory and design of universal low-voltage opamps

This chapter introduces the basic principles of low voltage universal opamp design. Universal low voltage opamps are amplifier architectures which operate with a constant-g/sub m/ from rail-to-rail and can be implemented in any complementary VLSI technology. Design examples in both MOS and bipolar technologies are described. Simulation and experimental results from test chips with a 3 V supply are also discussed.

Low-voltage four-quadrant analog multiplier

A novel design method for four-quadrant analog multiplier is presented. This method uses two current-mode maximum selecting circuits to combine the output currents of two MOS square-based multiplier cells. The proposed scheme nearly doubles the input voltage range.

LV complementary differential pair with programmable rail-to-rail constant-g/sub m/

In this paper a new differential pair architecture with programmable rail-to-rail constant-g/sub m/ is presented. Since the architecture adopts a signal processing method to obtain constant-g/sub m/ it can be implemented in any complementary VLSI technology and it functions regardless of transistor operating regions. An MOS implementation is discussed and is shown to operate in both weak and strong inversion, resulting in a programmable g/sub m/ over a very wide range.

A new implementation of constant-g/sub m/ op amp input stage for CMOS low voltage applications

In this paper we propose a new implementation method for the design of op amp input stage with rail-to-rail constant-g/sub m/. The new implementation is based on processing signal currents rather than handling DC tail currents. As a result, it is universal in that the constant-g/sub m/ can be obtained independent of input transistor types (MOS or bipolar) and their operating regions (weak or strong inversion for MOS and active for bipolar). To demonstrate the idea, a new MOS-type input stage has been designed with a 2-/spl mu/m CMOS process and simulation results of input stage transconductance are provided. The common mode input voltage can even exceed the positive and the negative rails by 300 mV.