Decimatorless continuous-time delta-sigma analog-to-digital receiver

This application claims the benefit under 35 U.S.C. 119(e) of the filing date of Provisional U.S. Application Ser. No. 62/049,851, entitled Decimatorless Continuous-Time-Delta-Sigma Analog-to-Digital Receiver, filed on Sep. 12, 2014, and expressly incorporated herein by reference, in its entirety.

1. Field of the Invention

The present invention generally relates to a communication receiver, and more particularly to a decimatorless continuous-time delta-sigma analog-to-digital receiver.

2. Description of Related Art

FIG. 1 shows a block diagram illustrated of a conventional receiver 100 that includes an automatic gain controller (AGC) 11 , an anti-aliasing filter (AAF) 12 , a delta-sigma modulator (DSM) 13 , a decimator (DEC) 14 and a demodulator 15 . The AAF 12 is commonly implemented by a low-pass filter that attenuates signals with frequencies higher than a cutoff frequency such that the signals may not be affected by frequency aliasing. In view of the fact that the sampling rate of a digital signal from the DSM 13 is usually higher than the cutoff frequency, the DEC 14 is ordinarily used to reduce the sampling rate.

Due to increasing miniaturization and cost down in the communication technology for electronic devices, particularly handheld electronic devices, a need has arisen to propose a novel communication receiver with more compact circuit area and reduced manufacturing cost.

In view of the foregoing, it is an object of the embodiment of the present invention to provide a decimatorless continuous-time delta-sigma analog-to-digital receiver without using a decimator and/or anti-aliasing filter, thereby reducing power consumption, circuit area and associated manufacturing cost.

According to one embodiment, a decimatorless continuous-time delta-sigma analog-to-digital receiver includes a continuous-time delta-sigma modulator (CTDSM) and a demodulator. The CTDSM receives a receiving signal and is configured to encode analog signals into digital signals. The demodulator receives a digital output of the CTDSM and is configured to recover information content from the receiving signal.

FIG. 1 shows a block diagram illustrated of a conventional receiver;

FIG. 2 shows a block diagram illustrated of a decimatorless continuous-time delta-sigma analog-to-digital receiver according to one embodiment of the present invention;

FIG. 3A shows a detailed block diagram of FIG. 2 illustrating a quadrature demodulator;

FIG. 3B shows a detailed block diagram of FIG. 2 illustrating another quadrature demodulator;

FIG. 4 shows a block diagram illustrated of a decimatorless continuous-time delta-sigma analog-to-digital receiver according to a first specific embodiment of the present invention; and

FIG. 5 shows a block diagram illustrated of a decimatorless continuous-time delta-sigma analog-to-digital receiver according to a second specific embodiment of the present invention.

FIG. 2 shows a block diagram illustrated of a decimatorless continuous-time delta-sigma analog-to-digital receiver (“receiver” hereinafter) 200 according to one embodiment of the present invention. In the embodiment, the receiver 200 may optionally include an automatic gain controller (AGC) 21 that receives a receiving (RX) signal and automatically controls an amplification level such that the controlled amplification level may lie in a linear working region of a latter stage or stages.

The receiver 200 of the embodiment may include continuous-time delta-sigma modulator (CTDSM) 22 that receives the original RX signal or the RX signal from the AGC 21 . The CTDSM 22 is configured to encode analog signals into digital signals. The CTDSM 22 , as typical continuous-time delta-sigma converters that employ a continuous-time noise-shaping filter (NSF), may possess low-pass filtering function. Accordingly, the anti-aliasing filter (AAF), such as the AAF 12 in FIG. 1 , of conventional delta-sigma analog-to-digital receivers may thus be omitted, therefore reducing power consumption, circuit area and associated manufacturing cost.

The receiver 200 of the embodiment may further include a demodulator 23 that receives a digital output of the CTDSM 22 . The demodulator 23 is configured to recover information content from the modulated RX signal. According to one aspect of the embodiment, the demodulator 23 works at a frequency that is at least higher than a cut-off frequency of the low-pass filtering mentioned above. As a result, the decimator, such as the DEC 14 in FIG. 1 , of conventional delta-sigma analog-to-digital receivers may thus be omitted, therefore reducing power consumption, circuit area and associated manufacturing cost.

FIG. 3A shows a detailed block diagram of FIG. 2 illustrating a quadrature demodulator (or phase mixer) 23 . In the figure, the digital output of the CTDSM 22 is phase mixed (or multiplied) by a pair of multipliers (or phase mixers) 231 . Specifically, the multipliers 231 respectively multiply the digital output of the CTDSM 22 by quadrature carriers (e.g., sinusoids), thereby resulting in phase mixed digital outputs, respectively. In the embodiment, the sinusoids, for example, a cosine wave cos [Ω c n] and a sine wave sin [Ω c n], are out of phase with each other by 90°. The phase mixed digital outputs are then summed by adders 232 , respectively, thereby resulting in recovered contents I and Q of the RX signal.

FIG. 3B shows a detailed block diagram of FIG. 2 illustrating another quadrature demodulator (or phase mixer) 23 . The quadrature demodulator 23 of FIG. 3B is similar to that in FIG. 3A with the exception that, the multipliers 231 multiply the digital output of the CTDSM 22 by windowed quadrature carriers (e.g., sinusoids), respectively, for decreasing effect of radio-frequency interference (RFI) on the quadrature carriers. Specifically, the windowed quadrature carriers are generated by multiplying the quadrature carriers with a window function w[n], which is a mathematical function that is zero-valued outside of a predefined interval. The window function w[n] of the embodiment may, for example, be Kaiser window, Hanning window, Hamming window or Blackman window.

FIG. 4 shows a block diagram illustrated of a decimatorless continuous-time delta-sigma analog-to-digital receiver (“receiver” hereinafter) 200 A according to a first specific embodiment of the present invention. In the embodiment, the CTDSM 22 may include a one-bit quantizer (not shown) as an output stage to generate a one-bit digital output of either 0 or 1. The quadrature demodulator 23 of the embodiment may include an I-demodulator 23 A and a Q-demodulator 23 B for generating recovered contents I and Q of the RX signal, respectively.

Specifically speaking, as the one-bit digital output is generated from the CTDSM 22 , the multipliers 231 in FIG. 3A / 3 B are no longer required. Instead, quadrature carrier (e.g., sinusoid) tables are used in the I-demodulator 23 A and the Q-demodulator 23 B. For example, a cosine wave table 2311 is used in the I-demodulator 23 A, and a sine wave table (not shown) is used in the Q-demodulator 23 B. In another embodiment, windowed quadrature carrier tables are used in the I-demodulator 23 A and the Q-demodulator 23 B.

A phase mixed digital output from the quadrature carrier table (e.g., the cosine wave table 2311 ) is then fed to a first input of a full adder (e.g., a 4-bit full adder in this example) 2321 . The content of the full adder 2321 is copied to a register (e.g., a 4-bit register in this example) 2322 . A carry of the register 2322 is used to trigger a carry counter (e.g., a ripple counter) 2323 , and an output (i.e., the content I or Q) of the carry counter 2323 is fed back to a second input of the full adder 2321 . Although not shown, the Q-demodulator 23 B has a structure similar to that of the I-demodulator 23 A with the exception that, the cosine wave table 2311 is replaced with a sine wave table.

FIG. 5 shows a block diagram illustrated of a decimatorless continuous-time delta-sigma analog-to-digital receiver (“receiver” hereinafter) 200 B according to a second specific embodiment of the present invention. The present specific embodiment is similar to that shown in FIG. 4 with the exception that, different bits of the digital output (e.g., cos [n][0], cos [n][1], cos [n][2] and cos [n][3]) are used to trigger corresponding carry counters 2324 - 2327 . Subsequently, outputs of the carry counters 2324 - 2327 are shifted (e.g., the output of the fourth carry counter 2327 is shifted by 3 bits, the output of the third carry counter 2326 is shifted by 2 bits, and the output of the second carry counter 2325 is shifted by 1 bit). The shifted outputs of the carry counters 2324 - 2327 are then summed up by a summer 2328 to generate recovered content I or Q of the RX signal. Although not shown, the Q-demodulator 23 B has a structure similar to that of the I-demodulator 23 A with the exception that, the cosine wave table 2311 is replaced with a sine wave table.

Although specific embodiments have been illustrated and described, it will be appreciated by those skilled in the art that various modifications may be made without departing from the scope of the present invention, which is intended to be limited solely by the appended claims.