Cmos Current Amplifiers

by Koli, Kimmo; Halonen, Kari A. I.

• ISBN13: 9781402070457
• ISBN10: 1402070454
• Format: Hardcover
• Copyright: 2002-07-01
• Publisher: Kluwer Academic Pub

Summary

CMOS Current Amplifiers; Speed versus Nonlinearity is intended as a current-amplifier cookbook containing an extensive review of different current amplifier topologies realisable with modern CMOS integration technologies. The seldom-discussed issue of high-frequency distortion performance is derived for all reviewed amplifier topologies using as simple and intuitive mathematical methods as possible. The topologies discussed are also useful as building blocks for high-performance voltage-mode amplifiers. So the reader can apply the discussed techniques to both voltage- and current-mode analogue integrated circuit design. For the most popular open-loop current-mode amplifier, the second-generation current-conveyor (CCII), a macro model is derived that, unlike other reported macromodels, can accurately predict the common-mode behaviour in differential applications. Similarly, this model is used to describe the nonidealities of several other current-mode amplifiers. With modern low-voltage CMOS-technologies, the current-mode operational amplifier and the high-gain current-conveyor (CCIIINFINITY perform better than various open-loop current-amplifiers. Similarly, unlike with conventional voltage-mode operational amplifiers, the large-signal settling behaviour of these two amplifier types does not degrade as CMOS-processes are scaled down. This book contains application examples with experimental results in three different fields: instrumentation amplifiers, continuous-time analogue filters and logarithmic amplifiers. The instrumentation amplifier example shows that using unmatched off-the-self components very high CMRR can be reached even at relatively high frequencies. As a filter application, two 1 MHz 3rd-order low-pass continuous-time filters are realised with a 1.2 mum CMOS-process. These filters use a differential CCIIINFINITY with linearised, dynamically biased output stages resulting in outstanding performance when compared to most OTA-C filter realisations reported. As an application example of nonlinear circuits, two logarithmic amplifier chips are designed and fabricated. The first circuit, implemented with a 1.2 m BiCMOS-process, uses again a CCII8 and a pn-junction as a logarithmic feedback element. With a CCII8 the constant gain-bandwidth product, typical of voltage-mode operational amplifiers, is avoided resulting in a constant 1 MHz bandwidth within a 60 dB signal amplitude range. The second current-mode logarithmic amplifier, realised in a 1.2 m CMOS-process, is based on piece-wise linear approximation of the logarithmic function. In this logarithmic amplifier, using limiting current amplifiers instead of limiting voltage amplifiers results in exceptionally low temperature dependency of the logarithmic output signal. Additionally, along with this logarithmic amplifier a new current peak detector is developed.

Table of Contents

Introduction to current-mode circuit techniques	1	(10)
Development of integration technologies	1	(1)
Motivation for current-mode circuit design	2	(1)
Evolution of current-mode building blocks	3	(1)
Adjoint principle	4	(2)
Scope of this book	6	(5)
Basic current amplifiers	11	(34)
Current-mirror	12	(26)
Nonidealities due to the channel length modulation	13	(3)
Nonidealities due the VT mismatch	16	(2)
High frequency nonidealities	18	(1)
Linear effects	18	(2)
Nonliearity in limited frequency ranges	20	(2)
Mirror as a feedback amplifier	22	(5)
Distortion reduction methods	27	(1)
Transconductance linearisation	27	(1)
Nonlinear current reduction	28	(1)
Nonlinear current cancellation	28	(3)
Noise and dynamic range	31	(2)
Other mirror topologies	33	(1)
Accurate current-mirror topologies for large signal amplitudes	33	(2)
Resistively compensated mirror	35	(3)
Current buffer	38	(7)
Linear nonidealities	39	(1)
Nonlinearity	40	(1)
Noise	41	(1)
Alternative topologies	41	(4)
Open-loop current amplifiers	45	(40)
First generation current-conveyor CCI	45	(10)
Linear nonidealities	46	(3)
Nonlinearity	49	(1)
Applications of the CCI	49	(1)
Push-pull CCI topologies	50	(4)
Low voltage CCI topologies	54	(1)
Second generation current-conveyor CCII	55	(25)
Linear nonidealities	57	(2)
CCII macromodel	59	(2)
Applications of the CCII	61	(6)
Nonlinearity of the class-A CCII	67	(1)
Alternative class-A CCII topologies	68	(4)
Push-pull CCII topologies	72	(1)
Basic operation of a push-pull CCII+	72	(2)
Basic operation of a push-pull CCII-	74	(1)
X-terminal impedance	75	(1)
Current gain nonlinarity	76	(4)
Third generation current-conveyor CCIII	80	(5)
Current-mode feedback amplifiers	85	(38)
Current-feedback operational amplifier	85	(12)
Closed loop bandwidth	87	(3)
Integrator implementations	90	(2)
Self-compensation of voltage followers	92	(1)
Common-mode rejection	93	(2)
CMOS implementations	95	(2)
Operational floating conveyor	97	(4)
Applications	98	(1)
Composite conveyors	99	(2)
Current-mode operational amplifiers	101	(6)
Distortion	102	(2)
Slew rate and full power bandwidth	104	(1)
Alternative topologies	105	(2)
High-gain current-conveyor CCII∞	107	(16)
Linear nonidealities	108	(2)
Applications	110	(3)
Distortion	113	(2)
Design example	115	(8)
System aspects of current-mode circuits	123	(30)
Input voltage-to-current conversion	123	(3)
Output current-to-voltage conversion	126	(3)
Differential voltage input structures	129	(24)
CMRR enhancement techniques	130	(1)
Common-mode bootstrapping	131	(1)
Output current subtraction	131	(4)
Composite conveyors	135	(2)
Differential current input structures	137	(1)
Single-ended to differential conversion	138	(3)
Noise in current-mode circuits	141	(1)
Class-A CMOS CCII+	141	(4)
Other low-gain conveyor topologies	145	(1)
High-gain current-conveyor	145	(3)
Other current-mode feedback amplifiers	148	(1)
General notes on current amplifier noise	149	(4)
Current-mode continuous-time filters	153	(60)
Integrator quality factor	154	(1)
Voltage-mode active-RC integrators	155	(2)
OTA-based integrators	157	(5)
The effects of process variation and temperature drift	158	(2)
Transconductance linearity	160	(2)
Integrators with MOS-resistors	162	(1)
Current-conveyor based filters	163	(4)
Current-mirror based filter	167	(5)
High-gain current-conveyor based filters	172	(4)
Multi-output current integrator with a linearised transconductor	176	(7)
Linearization by drain current difference	177	(4)
Linearisation by dynamic biasing	181	(2)
Design case: A 1 MHz current-mode low-pass filter	183	(25)
Filter building blocks	183	(1)
The transimpedance driver amplifier	184	(3)
Multiple-output linearised transconductance element	187	(1)
Temperature drift compensation of the integrator time constant	187	(3)
The first filter realisation	190	(2)
Integrator Q-enhancement	192	(3)
Experimental results	195	(3)
The second test chip	198	(3)
Alternate driver implementation	201	(4)
Experimental results	205	(3)
Final remarks	208	(5)
Current-mode logarithmic amplifiers	213	(46)
Diode-feedback logarithmic amplifiers	214	(16)
Voltage-mode operational amplifier based realizations	214	(2)
Design case: CCII∞ based logarithmic peak detector	216	(1)
BiCMOS implementation of a CCII∞	217	(1)
Logarithmic peak detector implementation	217	(5)
Post processing of the logarithmic output voltage	222	(7)
Final remarks on the design	229	(1)
Pseudologarithmic amplifiers	230	(22)
Limiting CMOS voltage amplifiers	231	(2)
Limiting CMOS current amplifiers	233	(2)
Accuracy of the pseudologarithmic amplifier	235	(1)
Amplitude detection in pseudologarithmic amplifiers	236	(1)
CMOS rectifiers	236	(2)
CMOS squarers	238	(1)
CMOS peak detectors	238	(4)
Design case: A 2.5 V CMOS pseudologarithmic current amplifier	242	(1)
Limiting amplifier	243	(2)
Current reference	245	(2)
Current peak detector	247	(1)
Experimental results	247	(5)
Other approaches	252	(7)
Current peak detector with enhanced discharging time constant adjustment	252	(7)
Conclusions	259	(2)
A Basic distortion definitions	261	(8)
Harmonic distortion	261	(1)
Intermodulation distortion	262	(1)
Distortion in feedback amplifiers	263	(6)
Distortion in quasi-static feedback amplifiers	263	(1)
Distortion in dynamic feedback amplifiers	264	(5)
B Distortion in push-pull current amplifiers	269	(6)
Class-A operation	269	(2)
Class-AB operation	271	(4)
C Distortion in CMOS operational amplifiers	275	(8)
Miller-compensated unbuffered operational amplifier	275	(4)
Folded cascode operational transconductance amplifier	279	(4)
D Distortion in a dual current-mirror integrator	283	(3)
Single-ended integrator	283	(3)
Differential integrator	286