A 3.6-MHz cutoff frequency CMOS elliptic low-pass switched-capacitor ladder filter for video communication

The high frequency (HF) behavior of the switched-capacitor (SC) LDI ladder filter is studied. This study shows that using low sampling frequency with respect to the cutoff frequency reduces the HF error due to the reduction in amplifier gain. Design techniques are also given for the HF SC filters, such as double-sampling scheme, a low sampling frequency with an exact synthesis algorithm, as well as a fast-settling folded-cascode amplifier. These techniques are applied to an experimental fifth-order elliptic SC filter fabricated in a 2-/spl mu/m CMOS technology. The experimental results show that a 3.6-MHz cutoff frequency is attained. All the capacitors are scaled down in order to reduce the setting time of the amplifiers. The active area of the filter is 0.9 mm/SUP 2/. The F/SUB sampling//F/SUB cutoff/ is only 5. The circuit operates from /spl plusmn/5 V and typically dissipates 80 mW when sampled at 18 MHz.     

A Novel Dual-Rate Sampling Switched-Capacitor Configuration and Its Application

In order to realize accurate bilinear transformation from s- to z-domain,a novelswitched-capacitor configuration is proposed in the light of principles of dual-rate sampling and chargeconservation,which has also been used for building a 5th-order elliptic lowpass filter.The filter issimulated and measured in typical 0.34 μm/3.3 V Si CMOS process models,special full differentialoperational amplifiers and CMOS transfer gate switches,which achieves 80 MHz sampling rate,17.8MHz cutoff frequency,0.052 dB maximum passband ripple,42.1 dB minimum stopband attenuation and74 mW quiescent power dissipation.At the same time,the dual-rate sampling topology breaks thetraditional restrictions of filter introduced by unit-gain bandwidth and slew rate of operational amplifiersand also improves effectively their performances in high-frequency applications.It has been applied forthe design of an anti-alias filter in analog front-end of video decoder IC with 15 MHz signal frequencyyet.     

A 500-nA sixth-order bandpass SC filter

A sixth-order bandpass switched-capacitor (SC) filter that requires only 500 nA of total supply current has been designed and fabricated in a 2-μm CMOS technology. The filter is part of an implantable device powered by a ±1.2-V battery; it can drive up to 30 pF of capacitive load and uses a 2-kHz sampling frequency. A substantial reduction in the power consumption has been achieved by using a novel amplifier time-sharing technique that allows the realization of an arbitrary number of biquadratic cells with only two amplifiers. Further power saving was obtained with the use of positive feedback in the amplifier input stage to enhance its transconductance. The prototype chip requires an area of 2200 mils²     

Switched-Capacitor Track-and-Hold Amplifiers With Low Sensitivity to Op-Amp Imperfections

This paper describes high-precision switched-capacitor (SC) track-and-hold amplifier (THA) stages. They use a novel continuous-time correlated double sampling (CDS) scheme to desensitize the operation to amplifier imperfections. Unlike earlier predictive-CDS amplifiers, the circuits do not need a sampled-and-held input signal for their operation. During the tracking period, an auxiliary continuous-time signal path is established, which predicts the output voltage during the holding period. This allows accurate operation even for low amplifier gains and large offsets over a wide input frequency range. Extensive simulations were performed to compare the performance of the proposed THAs with earlier circuits utilizing CDS. The results verify that their operation is far more robust than that of any previously described SC amplifiers     

基于OA-OTA的多功能电压模式滤波器

提出了一种由运算放大器（OA）和运算跨导放大器（OTA）构成的多功能电压模式滤波器。适当选定输入输出端，可以实现低通、高通、带通、带阻和全通滤波功能。由于电路仅含有源器件，因而适于全集成，且容易实现电路特性的电调节，中心频率及品质因数的有源灵敏度也很低，PSPICE仿真结果表明，提出的电路方案是可行的。     

SC filter circuit with decimation of sampling frequency

Realisation of a switched-capacitor filter circuit with decimation of the input sampling frequency is proposed. The circuit, which is compensated for the influence of parasitic capacitances, is useful as an input stage of an SC filter. It can also be used for the realisation of an integrator, based on Simpson's rule.     

A micropower fourth-order elliptical switched-capacitor low-pass filter

A micropower fourth-order elliptical switched-capacitor (SC) low-pass filter for biomedical applications has been designed and measured. The charge transfer error of an SC integrator using a transconductance amplifier is discussed. Also first-order noise and PSRR calculations are performed and compared with the results of simulations and measurements. The measurements show that by careful optimization of the gain bandwidth, slew rate, and gain of the amplifiers, high-performance low-power SC filters can be constructed. The cutoff frequency of the filter is 5 kHz, the ripple in the passband is 0.27 dB, and stopband rejection is 49 dB. The power consumption of the filter is 190 /spl mu/W with /spl plusmn/2.5-V power supplies. The dynamic range of the filter is 75 dB, and the total harmonic distortion over the whole passband range is below 0.25% for a 2-V/SUB pp/ input signal. The PSRR of the filter is above 40 dB at frequencies below 3 kHz.     

Adaptor realisations for wave switched-capacitor filters with reduced capacitance spread

The design of wave SC adaptors with very low capacitance spread is described and illustrated for the case of the unit-element cascade filter. The adaptors are canonic in the number of operational amplifiers and are parasitic-insensitive.     

用于光通信系统的BiCMOS F/V转换器

设计了一种由3运放A_1、A_2和A_3组成的BiCMOS频率/电压(F/V)转换器,其中A_1、A_2设计成共源一共源CMOS运放,而低通滤波器(LPF)中的A_3采用BiCMOS运放.优选了整个F/V转换器的元器件参数,并采取了提速和降耗等措施.实验结果表明,所设计的转换器输入至LPF的脉冲信号频率f_2与输入信号频率f_i相等,且该转换器输出电压平均值U_o与f_i成正比;它可在4 Hz≤f_i≤10 kHz的范围内工作,其综合性能指标--延迟-功耗积约为1.09 nJ,转换线性度仅为1.7×10~(-2),因而特别适用于低功耗、高线性度的光纤通信和光电检测系统中.

Abstract：

A BiCMOS F/V converter including 3 operational amplifiers A_1, A_2 and A_3 was designed, in which A_1 and A_2 were double common-source CMOS operational amplifiers and the low-pass filter (LPF) A_3 was a BiCMOS one. The parameters of the entire converter were optimized and some measures were adopted such as raising speed and reducing power-consumption. The experimental results show that the its input pulse signal frequency f_2 to the LPF is equal to the input signal frequency f_i, and its average-output-voltage (U_o) is in direct proportion to f_i. The designed converter can work properly within 4 Hz～10 kHz, and its delay-power product is about 1.09 nJ, and the conversion linearity is only 1.7 X 10~(-2). With these characteristics, the designed converter is very suitable for low-consumption and high-linearity fiber-optic communications and photoelectric detection systems.     

Exploiting the high-frequency performance of low-voltage low-power SC filters

This paper investigates the design of low-voltage low-power switched-capacitor (SC) filters for high-frequency applications by using the clock-booster approach. In particular, our proposed SC filter architecture uses single-ended double-sampling integrator cells based on low-voltage operational transconductance amplifiers which take advantage of dynamic biasing and the clock-booster technique to drive the switch transistors. To validate its high-frequency capability, two low-pass elliptic SC filters respectively with a corner frequency of 6 and 8-MHz, were designed in a 0.35-/spl mu/m CMOS process. Both are suitable for telecom applications and can operate with a power supply as low as 1.5 V, while dissipating 11 mW. Measurements showed that for an output amplitude of 1 V/sub pp/, their total harmonic distortions were maintained well below -40 dB in their bandwidths. Comparisons with other SC filter implementations in the literature, which highlight the quality of our implementation are also provided.     

Comments on `New monolithic switched-capacitor differentiators withgood noise rejection'

For the original article see ibid., vol.24, no.1, p.177-80 (1989). The commenter notes that the basic inverting SC differentiator described by C.-Y. Wu et al. was proposed by B.J. Hosticka and G. Moschytz (1979), and the behavior of the earlier circuit is discussed. The commenter also points out that the operational amplifiers in the SC filter of Wu et al. must slew in each φ₁ phase from the signal value to ground, thus limiting the maximum usable clock frequency     

Canonic adaptor realisations for wave switched-capacitor filters

The principles of the design of canonic wave SC adaptors based on parasitic-insensitive voltage storage and subtraction are described. The adaptors may be used in any filter configuration and have a minimum number of operational amplifiers.     

A novel two-amplifier universal active switched-capacitor filter

A switched-capacitor (SC) filter circuit realizing low-pass (LP), high-pass (HP), and bandpass (BP) transfer functions is described. This circuit uses only two operational amplifiers (OAs) and is bottom-plate stray-insensitive.     

Real-time programmable low power SC bandpass filter

A real-time programmable switched capacitor (SC) second-order bandpass filter is presented. It is based on the voltage inverter switch (VIS) principle using inverse recharging devices. These devices are realized with dynamic amplifiers in order to achieve low power dissipation. The filter contains only grounded or virtually grounded network capacitances and, therefore, it is insensitive to the parasitic capacitances between the bottom plate of the implemented MOS capacitors and the substrate. The circuit offers digital programming capability (two Q factors and three center frequencies) and low power dissipation (185 /spl mu/W at a sampling frequency of 8 kHz and with a power supply voltage of 10 V). The filter has been integrated in CMOS metal-gate technology.     

High-performance active bandpass filter using current-feedback amplifiers

An accurate current feedback amplifier based high-Q active bandpass filter whose centre frequency is independently variable over a wide frequency range is presented. The basic circuit has the important advantage that access to the Z node of the current-feedback amplifier is not required, as is the case with many existing current-feedback amplifier filter circuits. Additionally, the circuit can be implemented with operational amplifiers, though for high Q the Q? and ω₀? variabilities are 62% better with current-feedback amplifiers than with operational amplifiers. Experimental results are presented which are in good agreement with expected theory.     

Transient analysis of charge-transfer in SC filters-gain error and distortion

In switched-capacitor (SC) circuits, op amps often slew during the charge-transfer transient. When this happens, the charge-transfer error is no longer proportional to the input signal. The charge-transfer transient is studied in detail, taking into account the slewing behavior of the amplifiers. Analytical expressions are obtained for the charge-transfer error of an SC integrator. In switched-capacitor signal processing, the harmonic distortion can be defined as the harmonic distortion of the envelope of the sampled-data sequence. A Fourier analysis is carried out on the sampled-data sequence corrupted by the charge-transfer error due to slewing of the operational transconductance amplifiers. Analytical expressions are derived for harmonic distortions of an SC integrator. Analysis of the results shows that slew-induced harmonic distortion can be minimized by using large transconductance. It is possible to design SC filters with low power consumption and low harmonic distortion without resorting to class AB amplifiers.     

New Universal Filter with One Input and Five Outputs Using Current-Feedback Amplifiers

A new universal voltage-mode second-order filter circuit is presented. The circuit uses five current-feedback operational amplifiers, two grounded capacitors three grounded resistors and three floating resistors. The circuit can realize all the standard filter functions; lowpass, highpass, bandpass, notch and allpass, without changing the passive elements. The proposed circuit enjoys independent grounded-resistance-control of the natural frequency and the bandwidth, low output impedances, high input impedance as well as low active and passive sensitivities.     

A simple technique to evaluate the noise spectral density in operational amplifier based circuits using the adjoint network theory

We use the adjoint network theory to get quick estimates of the noise contributed by various elements in linear time-invariant opamp based circuits. The noisy operational amplifier is represented using a or with an input referred noise voltage and current source. The adjoint model for this representation is derived. This makes the noise analysis of operational amplifier based circuits very simple and the contribution of the operational amplifiers to the output noise can be obtained very often by inspection. The method is applicable to amplifiers, active RC and MOSFET-C filters. Examples of circuits analyzed include the universal active filter and gyrator topologies.     

Meander-channel c.c.d. (m.c.c.d.) recursive filter

A modified input-weighting concept for a c.c.d. recursive filter is proposed; it has been implemented using an m.c.c.d. with a complementary input scheme which provides net weighting coefficients. This improved structure requires neither operational amplifiers nor resistors. The operation and performance of the fabricated 2nd-order bandpass filter are presented.     

A tunable filter using amplifier pole

A circuit consisting of two periodically operated switches, potentiometers, resistors, and compensated operational amplifiers, but not containing external capacitors, is proposed for the realization of a second-order bandpass and low-pass filter. The filter is electronically tunable and the natural frequency of the filter varies linearly with the width of the pulses controlling the FET switches.