Proceedings Article•
Accurate characterization of integrated continuous-time filters
01 Jan 2007-Vol. 42, Iss: 8, pp 1758-1766
TL;DR: When compared to conventional frequency response measurement methods, the proposed techniques show a significantly enhanced measurement accuracy in the stopband, while being less sensitive to package characteristics.
Abstract: ·We present techniques for accurately characterizing the frequency response and noise spectral density of integrated continuous-time filters. A 75-MHz fifth-order Chebyshev Gm-C ladder filter designed in a 0.35-μm CMOS process and packaged in a 40-pin DIP is used as a test vehicle to validate the ideas proposed in this work. When compared to conventional frequency response measurement methods, the proposed techniques show a significantly enhanced measurement accuracy in the stopband, while being less sensitive to package characteristics.
Citations
More filters
TL;DR: An all-pass filter architecture that can be generalized to high orders, and can be realized using active circuits is proposed, and a compact true-time-delay element with a widely tunable delay and a large delay-bandwidth product (DBW) is demonstrated.
Abstract: An all-pass filter architecture that can be generalized to high orders, and can be realized using active circuits is proposed. Using this, a compact true-time-delay element with a widely tunable delay and a large delay-bandwidth product (DBW) is demonstrated. This is useful for beamforming and equalization in the lower GHz range where the use of $LC$ or transmission line-based solutions to realize large delays is infeasible. Coarse tuning of delay is realized by changing the filter’s order while keeping the bandwidth constant and fine tuning is implemented by changing the filter’s bandwidth utilizing the delay-bandwidth tradeoff. A test chip fabricated in 0.13 $\mu \text{m}$ CMOS process demonstrates a delay tuning range of 250 ps–1.7-ns, over a bandwidth of 2 GHz, while maintaining a magnitude deviation of ±0.7 dB. The filter achieves a DBW of 3.4 and a delay per unit area of 5.8 $\mathrm {ns/mm^{2}}$ . The filter has a worst case noise figure of 23 dB, and −40 dB intermodulation (IM3) distortion for 37 mVppd inputs. The chip occupies an active area of 0.6 mm2, and dissipates 112 mW–364 mW of power between its minimum and maximum delay settings. Computed radiation pattern with four antennas spaced $\mathrm {\lambda _{fmax}}/2$ apart shows ±90° beam steering off broadside.
67 citations
Cites background or methods from "Accurate characterization of integr..."
...The polarity of the output is changed by enabling/disabling the control bit, FLIP, which helps in canceling the inputoutput feedthrough [17]....
[...]
...The technique described in [17] has been used to de-embed the noise and the frequency dependent effects of the measurement paths....
[...]
TL;DR: The Gm-assisted OTA-RC technique is explored, which is a way of combining GM-C and active-RC integrators in a manner that enhances the linearity and speed of the latter, while adding negligible extra noise or power dissipation.
Abstract: The linearity of conventional active-RC filters is limited by the operational transconductance amplifiers (OTAs) used in the integrators. Transconductance-capacitance (Gm-C) filters are fast and can be linear- however, they are sensitive to parasitic capacitances. We explore the Gm-assisted OTA-RC technique, which is a way of combining Gm-C and active-RC integrators in a manner that enhances the linearity and speed of the latter, while adding negligible extra noise or power dissipation. Measurements from a fifth-order Chebyshev filter with 20 MHz bandwidth, designed in a 0.18 μ m CMOS process, demonstrate the efficacy of Gm-assistance in an active-RC integrator.
66 citations
Cites background from "Accurate characterization of integr..."
...To prevent measurement errors due to package feedthrough, the gain of the buffers can be multiplied by 1 [14]....
[...]
TL;DR: The principle of ldquoconstant capacitance scalingrdquo is applied to the opamp and the integrating resistors so that the shape of the frequency response is maintained when the bandwidth is scaled over a 7 times range.
Abstract: We propose a circuit technique that enables the realization of widely programmable high-frequency active RC filters in CMOS technology. A fifth-order Chebyshev ladder filter having a digitally programmable 3-dB bandwidth (from 44 to 300 MHz) is used as a vehicle to validate our ideas. The opamp uses feedforward compensation for achieving high dc gain and wide bandwidth. The integrating resistors are realized as a series combination of a triode-operated MOSFET and a fixed polysilicon resistor. A charge-pump-based servo loop servoes the integrating resistor to a stable off-chip resistor. The principle of ldquoconstant capacitance scalingrdquo is applied to the opamp and the integrating resistors so that the shape of the frequency response is maintained when the bandwidth is scaled over a 7 times range. The filter core, designed in a 0.18-mum CMOS process, consumes 54 mW from 1.8-V supply and has a dynamic range of 56.6 dB.
62 citations
Cites background or methods from "Accurate characterization of integr..."
...In this paper, we propose an improvement over the test method proposed in [19]....
[...]
...(b) Technique with increased accuracy [19]....
[...]
...This is used to cancel the effect of package feedthrough, as discussed in [19]....
[...]
...(c) Improvement over [19] to increase buffer linearity, as well as cancel package feedthrough....
[...]
...In a recent work [19], it was shown that the measurement technique of [18] is accurate in the filter passband but is prone to error in the filter stopband....
[...]
TL;DR: This paper presents a differential fourth-order low-pass filter suitable for electrocardiography (ECG) acquisition formed by cascading two compact and power-efficient biquads operating in the subthreshold region that performs comparably to the recent state-of-the-art nanowatt-class low- pass filter.
Abstract: This paper presents a differential fourth-order low-pass filter suitable for electrocardiography (ECG) acquisition. It is formed by cascading two compact and power-efficient biquads operating in the subthreshold region. Each biquad combines two capacitors and a flipped voltage follower circuit. The filter attains a cutoff frequency adjustable to cover the entire range of ECG (150–250 Hz). The filter prototype has been fabricated in a 0.35- $\mu \text{m}$ CMOS technology. It occupies an area of $362\,\,\mu \text {m} \times 466 \,\,\mu \text{m}$ and operates from a 0.6-V supply. Measurements confirm that the filter consumes 0.9-nW static power for a 101-Hz cutoff frequency and contributes the input-referred noise of 46.27 $\mu \text{V}_{\mathbf {rms}}$ . For a 60-Hz input frequency, the filter achieves a dynamic range of 47 dB where the third-harmonic distortion of −60 dB is produced. This leads to the figure of merit of $46.5 \times 10^{-18}$ J. When the chip area is also concerned, the proposed filter performs comparably to the recent state-of-the-art nanowatt-class low-pass filter.
42 citations
Cites background from "Accurate characterization of integr..."
...5 pF that creates an extra feed-forward path allowing the input signal to travel to the output terminal directly [19]....
[...]
TL;DR: A low-distortion active filter is realized using current-efficient feedforward-compensated operational amplifiers in the integrators and feedforward current injection in the summing amplifier to counter process variations and set the bandwidth accurately.
Abstract: A low-distortion active filter is realized using current-efficient feedforward-compensated operational amplifiers in the integrators and feedforward current injection in the summing amplifier. A third-order elliptic low-pass filter with two possible bandwidth settings of 17 and 8.5 MHz consumes 1.8 mW from a 1.8-V supply and occupies 0.17 mm2 in a 0.18- μm CMOS process. The measured maximum signal-to-noise and distortion ratios at the two bandwidth settings are 50.5 and 52.5 dB, respectively. The corresponding third-order intermodulation intercept points (IIP3) are +28.2 and +30.8 dBm. Automatic tuning is used at the startup to counter process variations and set the bandwidth accurately.
21 citations
Cites background from "Accurate characterization of integr..."
...external feedthrough can be cancelled, and the transfer function of the filter can be accurately measured [9]....
[...]
References
More filters
TL;DR: In this article, a linear, tunable integrator for very high-frequency integrated filters can be made, which has good linearity properties and non-dominant poles in the gigahertz range owing to the absence of internal nodes.
Abstract: CMOS circuits for integrated analog filters at very high frequencies, based on transconductance-C integrators, are presented. First a differential transconductance element based on CMOS inverters is described. With this circuit a linear, tunable integrator for very-high-frequency integrated filters can be made. This integrator has good linearity properties and nondominant poles in the gigahertz range owing to the absence of internal nodes. The integrator has a tunable DC gain, resulting in a controllable integrator quality factor. Experimental results of a VHF CMOS transconductance-C low-pass filter realized in a 3- mu m CMOS process are given. Both the cutoff frequency and the quality factors can be tuned. The cutoff frequency was tuned from 22 to 98 MHz and the measured filter response is very close to the ideal response of the passive prototype filter. Furthermore, a novel circuit for automatically tuning the quality factors of integrated filters built with these transconductors is described. >
674 citations
"Accurate characterization of integr..." refers methods in this paper
...One advantage of the technique proposed in [1] is that it needs only magnitude measurements, which can be made using a spectrum analyzer with a tracking generator (note that the VNA technique described in the previous section needed both magnitude and phase)....
[...]
...The common technique, originally proposed in [1], employed for on-chip filter characterization is shown in Fig....
[...]
TL;DR: In this paper, the authors present design considerations for programmable high-frequency continuous-time filters implemented in standard digital CMOS processes, where accumulation MOS capacitors are used as integrating elements to reduce area, and a constant-capacitance scaling technique is employed to ensure that even parasitic capacitances remain invariant when transconductors are switched in and out of the filter.
Abstract: We present design considerations for programmable high-frequency continuous-time filters implemented in standard digital CMOS processes. To reduce area, accumulation MOS capacitors are used as integrating elements. The filter design problem is examined from the viewpoint of programmability. To allow frequency scalability without deterioration of noise performance and of the frequency response shape, we employ a technique called "constant-capacitance scaling," which assures that even parasitic capacitances remain invariant when transconductors are switched in and out of the filter. This technique is applied to the design of a programmable fourth order Butterworth continuous-time filter with a bandwidth programmable from 60 to 350 MHz implemented in a 0.25-/spl mu/m digital CMOS process. The filter has a dynamic range of 54 dB, dissipates 70 mW from a 3.3-V supply, and occupies an area of 0.15 mm/sup 2/.
140 citations
"Accurate characterization of integr..." refers background or methods in this paper
...Measurements made on the fourth-order Butterworth filter reported in [3] were only accurate for frequencies where the attenuation was less than about 60 dB....
[...]
...The architecture of the filter was based on [3]....
[...]
...When M8–M9 are turned off, a dummy pair Md1–Md2 is turned on, so that the impedance at nodes and remain the same [3]....
[...]
TL;DR: The automated noise measurement system used for data acquisition and the mathematical basis for it are described, and the validity of the de-embedding approach is established with extensive experimental data obtained on three MESFETs and a pseudomorphic HEMT.
Abstract: A method based on the noise correlation technique and its applications is described. The package, which need not be reciprocal, may consist of an arbitrary interconnection of linear passive elements at thermal equilibrium. Only the terminal admittance properties of the package need be known. However, in certain special cases which lead to singular submatrices of the admittance matrix, the method is inapplicable. This situation can occur when elements such as isolators are part of the package. The necessary theoretical foundation and experimental techniques to enable workers not familiar with the field to assemble the software and laboratory setup for two-port noise de-embedding is provided. The automated noise measurement system used for data acquisition and the mathematical basis for it are described in some detail. The validity of the de-embedding approach is established with extensive experimental data obtained on three MESFETs and a pseudomorphic HEMT. >
130 citations
Additional excerpts
...[7] and [8] present techniques to measure the noise spectral densities of packaged two-ports....
[...]
TL;DR: A bipolar seventh-order 0.05 degrees equiripple linear phase (constant group delay) transconductance-capacitor (g/sub m/-C) low-pass filter with a cutoff frequency (f/sub c/) tunable between 2 and 10 MHz is presented.
Abstract: A bipolar seventh-order 0.05 degrees equiripple linear phase (constant group delay) transconductance-capacitor (g/sub m/-C) low-pass filter with a cutoff frequency (f/sub c/) tunable between 2 and 10 MHz is presented. Programmable equalization up to 9 dB at f/sub c/ is also provided. Total harmonic distortion at 2 V/sub p-p/ is less than 1%, with a dynamic range equal to 49 dB. Nominal power consumption from a single 5-V supply is 135 mW. The circuit also has a low-power mode ( >
104 citations
"Accurate characterization of integr..." refers background or result in this paper
...However, in our experience, as well as experimental results reported in the literature (for example [ 2 ]‐[6]), the accuracy of the measurement in the stopband of the filter is poor....
[...]
...The equiripple group delay filter of [ 2 ] has a measured stopband attenuation that does not reduce below 60 dB beyond 40 MHz....
[...]
TL;DR: In this paper, a third-order G/sub m/-C Butterworth low-pass filter is proposed for zero-IF radio receiver architecture for multimode mobile communications, with a cutoff frequency range from 50 kHz to 2.2 MHz.
Abstract: A third-order G/sub m/-C Butterworth low-pass filter implementing G/sub m/-tuning and G/sub m/-switching to maximize the tuning range is described. This filter is intended to be used as a channel-selection/anti-aliasing filter in the analog baseband part of a zero-IF radio receiver architecture for multimode mobile communications. Its G/sub m/-switching feature allows extending the tuning range and adapting the power consumption. The filter's cutoff frequency ranges from 50 kHz to 2.2 MHz. An Input IP3 of up to +18 dBV/sub p/ is achieved, for a total worst-case power consumption of 7.3 mW for both I and Q paths, and an effective area of less than 0.5 mm/sup 2/ in a 0.25-/spl mu/m SiGe BiCMOS process. A new figure of merit is introduced for comparison of published low-pass tunable filters including noise, linearity, and tuning range.
87 citations
"Accurate characterization of integr..." refers background or result in this paper
...Test setup problems are not restricted to high-frequency filters—measurements of the baseband Butterworth filters reported in [ 6 ] show a deviation from the ideal beyond a few megahertz, where the attenuation is greater than 70 dB. Usually, such problems are attributed to the “quality of the test setup”, implicitly assuming that the filter itself has no problems....
[...]
...However, in our experience, as well as experimental results reported in the literature (for example [2]‐[ 6 ]), the accuracy of the measurement in the stopband of the filter is poor....
[...]