Miscellaneous active electrical nonlinear devices – circuits – and – Specific input to output function – Logarithmic
Reexamination Certificate
2001-02-07
2004-04-13
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific input to output function
Logarithmic
C327S341000, C327S552000, C327S563000, C330S257000, C330S288000, C330S303000
Reexamination Certificate
active
06720817
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the field of continuous-time integrated circuits filters. More particularly, it relates to an all NPN class-AB log-domain integrator.
BACKGROUND OF THE INVENTION
Companding can be used to maintain reasonable dynamic range (DR) in integrated analog signal processors where the allowable voltage swings are limited by the low-voltage supply requirements of modem low-power applications. Syllabic companding is discussed in Y. Tsividis, “Externally linear, time-invariant systems and their application to companding signal processors,” IEEE Trans. Circuits Syst. II, vol. 44, no. 2, pp. 65-85, February 1997. As shown in FIG.
1
(
a
) for the case of syllabic companding, the input signal is compressed before being processed, which ensures signal integrity over a large range of input levels. At the output, the signal is expanded to restore its dynamic range. This can result in a higher DR compared to conventional analog signal processors. Y. Tsividis et al. discuss this issue in “Companding in signal processing,” Electronic Letters, vol. 26, no. 17, pp, 1331-1332, August 1990. Unlike the conventional processors) this does not come at the expense of increased power dissipation or chip area for a given bandwidth,
Log-domain filters, which constitute a special class of instantaneous companding signal processors are discussed in Y. Tsividis, “Externally linear, time-invariant systems and their application to companding signal processors,” IEEE Trans. Circuits Syst. II, vol. 44, no. 2, pp. 65-85, February 1997. They have already been used to realize programmable integrated filters reaching cutoff frequencies up to 220-435 MHz. For example, see M. N. El-Gamal and G. W. Roberts, “Very high-frequency log-domain bandpass filters,” IEEE Trans. Circuits Syst. II, vol. 45, no. 9, pp. 1188-1198, September 1998. and D. R. Frey, “Log domain filtering for RF applications,” IEEE J. Solid-State Circuits, vol. 31, no. 10, pp. 1468-1475, October 1996. The power consumption of those filters is relatively high due to their 2.7-5 V power supplies, and the dynamic ranges are limited by class A operation. Two low-voltage class AB implementations have already been proposed. The first one is based on the bipolar integrator introduced by Seevinck (See E. Seevinck, “Companding current-mode integrator: A new circuit principle for continuous-time monolithic filters,” Electronics Letters, vol. 26, no. 24, pp. 2046-2047, November 1990.), and the second one is the BiCMOS realization proposed by Punzenberger and Enz (See M. Punzenberger and C. C. Enz, “A 1.2 V BiCMOS class AB log-domain filter,” ISSCC Dig. Tech. Papers, pp. 56-57, February 1997.). Seevinck's circuit is a good candidate for high-frequency applications, since it employs N-type devices only in the signal path. However, it needs a minimum supply voltage of ≈1.7 V, compared to the 1.2 V requirement of the BiCMOS circuit of Punzenberger and Enz.
There is therefore a need for a 1.2 V bipolar realization which does not employ PMOS or PNP devices in the signal path, making it suitable for VHF applications.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide very high-frequency (VHF) and low-voltage continuous-time filters with cutoff frequencies in the 30-100 MHz range, suitable for low-power applications with moderate linearity and SNR specifications (e.g. high-frequency digital communications), and requiring a wide frequency tuning range.
A further object of the present invention, is to propose a simple, common-mode interference-resistant, class AB log-domain integrator, suitable for implementation in low-cost bipolar processes.
Still another object of the present invention, is to make an integrator which is suitable for realizing low-voltage filters with reasonable linearity and SNR with compatible all-NPN low-distortion input and output interface stages.
A further object of the present invention is to realize high-frequency programmable filters.
Two variations of a continuous-time instantaneous companding filter are integrated in a 25 GHz bipolar process. Their −3 dB frequencies are timable in the ranges of 1-30 MHz and 30-100 MHz. The dc gains are controllable up to 10 dB, The measured dynamic ranges for a 1% THD are 62.5 dB and 50 dB, for the 30 MHz and 100 MHz filters respectively. At maximum cutoff frequencies, the filters dissipate 6.5 mW from a 1.2 V supply.
The integrator preferably has the following characteristics:
1. It does not employ p-type transistors (e.g., PNP or PMOS transistors) in the signal path. This has the following two major advantages:
* The integrator maximum operating speed is not limited by the low-frequency p-type devices often provided in IC technologies. It is therefore suitable for high-frequency applications.
*Its implementation and use is not limited to the BiCMOS IC technologies or to the special bipolar IC technologies featuring high-quality PNP transistors. The integrator can therefore be used to implement filters in the many low-cost bipolar technologies available, giving it an edge over other circuits employing p-type devices in the signal path.
2. The integrator does not respond to a common-mode signal applied to its positive and negative input ports simultaneously. This makes it robust against interference, which is a very desirable feature in an IC environment, especially if digital circuitry share the same substrate with the integrator.
3. The integrator can operate from very low supply voltages, as low as 1.2 V. This makes it suitable for low-power applications (e.g. portable devices).
4. It is class-AB: It can therefore handle large signal currents despite of the limited supply voltage. This considerably extends its Dynamic Range (DR) and SNR.
5. It has a logarithmically nonlinear transfer function, making it suitable to be used in implementing the specific class of continuous-time filters called “log-domain filters”. The latter are known to result in a high SNR compared to conventional filters.
The first two features discussed above (points 1, and 2.) are unique to the integrator circuit proposed in this invention. This gives it a substantial edge over the state-of-the-art BiCMOS, class-AB, 1.2 V integrator circuit. The latter is limited to the technology it can be used with, i.e. BiCMOS or high quality bipolar, in order to ensure high performance. It is also limited in operating speed: A prototype filter built using this integrator reached a maximum operating speed of only 1 MHz, compared to a similar prototype built with the proposed integrator, which reached a speed of 100 MHz. And finally, the conventional circuitry is more sensitive to interfering signals than the circuit proposed herein.
In addition to the integrator, a new input preprocessing stage is proposed, and a compatible output stage that complements it is also provided such that a complete filter can be implemented. The input stage converts a differential input signal into two “strictly positive” complementary signals. Similar to the integrator, it uses a novel all-NPN circuit that can also operate from a supply voltage as low as 1.2 V.
Accordingly, a first broad aspect of the present invention is to provide a log-domain integrator. The log-domain integrator preferably comprises:
a positive compressed input voltage and a negative compressed input voltage;
a positive compressed output voltage and a negative compressed output voltage;
a ground and a reference voltage;
a first capacitor and a second capacitor;
a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a sixth transistor, a seventh transistor, an eighth transistor, a ninth transistor, a tenth transistor, an eleventh transistor, a twelfth transistor, a thirteenth transistor, a fourteenth transistor;
a first current source, a second current source, a third current source, a fourth current source, a fifth current source, a sixth current source, a seventh current source, an eighth current source, a ninth current source, a tenth current source, an eleventh
(Ogilvy Renault)
Anglehart James
Callahan Timothy P.
McGill University
Nguyen Minh
LandOfFree
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