Quadrature modulator with integrated distributed RC filters

• US 5,530,722 A
• Filed: 09/14/1994
• Issued: 06/25/1996
• Est. Priority Date: 10/27/1992
• Status: Expired due to Term

• Current Assignee: Unwired Planet LLC (JP Morgan Chase & Co)
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Dent, Paul W.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Kim, Kevin
• Application Number:
  US08/305,702
• Time in Patent Office: 650 Days
• Field of Search: 375/295, 375/298, 375/261, 375/269, 375/271, 375/272, 375/273, 375/279, 375/280, 375/281, 375/302, 375/303, 375/308, 375/312, 332/103, 332/149
• US Class Current: 375/298
• CPC Class Codes: H03C 1/542 comprising semiconductor devices with at least three electrodes
• CPC Class Codes: H03H 1/02 of RC networks, e.g. integrated networks
• CPC Class Codes: H03H 11/1204 Distributed RC filters
• CPC Class Codes: H03M 3/024 using syllabic companding, e.g. continuously variable slope delta modulation [CVSD]
• CPC Class Codes: H04B 1/0003 Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain digital baseband systems H04L25/00; digital modulation/demodulation H04L27/00; CDMA H04B1/707; TDMA H04B7/2643; image transmission H04N5/00
• CPC Class Codes: H04B 1/0014 using DSP [Digital Signal Processor] quadrature modulation and demodulation
• CPC Class Codes: H04B 1/0021 Decimation, i.e. data rate reduction techniques H04B1/0025 takes precedence
• CPC Class Codes: H04B 1/0039 using DSP [Digital Signal Processor] quadrature modulation and demodulation
• CPC Class Codes: H04B 1/26 for superheterodyne receivers multiple frequency-changing H03D7/16
• CPC Class Codes: H04B 1/40 Circuits
• CPC Class Codes: H04L 25/03834 using pulse shaping
• CPC Class Codes: H04L 27/2017 in which the phase changes are non-linear, e.g. generalized and Gaussian minimum shift keying, tamed frequency modulation H04L27/201 takes precedence
• CPC Class Codes: H04L 27/2064 using microwave technology

Abstract

A quadrature modulator for generation of complex modulated signals includes a unique pair of balanced, low-pass filters which, through a switching arrangement for switching into and out of the circuit distributed RC line sections and corresponding ground resistances are able to redress problems associated with manufacturing tolerances.

Claims

1. A quadrature modulator for the generation of complex modulated signals, comprising:

a digital sample generator producing a sequence of numerical value pairs respectively representing a real and imaginary modulating waveform;

a delta-sigma convertor circuit converting said sequence of pairs of numerical values to a high bit rate stream I representing said real waveform and a high bit rate stream Q representing said imaginary waveform, and additionally a bitstream I being the complement of I and a bitstream Q being the complement of Q;

a pair of balanced, low-pass filters each having two inputs accepting said bitstreams I, I and Q, Q respectively and each having two output lines providing balanced, filtered I and Q signals;

a first balanced modulator having a first, balanced input including two lines connected to said balanced, filtered I signals, and a second input connected to a cosine carrier frequency signal generator;

a second balanced modulator having a first, balanced input including two lines connected to said balanced, filtered Q signals, and a second input connected to a sine carrier frequency generator; and

an adder for adding said first and second balanced modulator outputs together.

2. A quadrature modulator according to claim 1 wherein each of said first and second balanced modulators is responsive to a difference in voltages presented to the two lines of its said balanced input and unresponsive to changes in the sum of said voltages.

3. A quadrature modulator according to claim 1 wherein said pair of balanced, low-pass filters attenuate to a desired level a balanced mode signal, being defined as the difference in voltages between said two input lines or two output lines, and attenuate to a different degree or not at all a common-mode signal, being defined as the sum of the voltages on said two input lines or two output lines.

4. A quadrature modulator according to claim 3 wherein said balanced, low-pass filters are comprised essentially of resistive and capacitive elements.

5. A quadrature modulator according to claim 3 wherein said pair of balanced, low-pass filters include resistive and capacitive elements formed by depositing resistive and dielectric films on a substrate.

6. A quadrature modulator according to claim 5 wherein said substrate is formed of a material selected from the group consisting of silicon, alumina, gallium arsenide, sapphire, and polyamide.

7. A quadrature modulator according to claim 5 wherein said substrate is a semiconductor material and said balanced modulators are constructed on said substrate using transistors formed in said semiconductor material.

8. A quadrature modulator according to claim 3 wherein said balanced, low-pass filters are constructed by use of distributed RC lines having a resistive pattern deposited over a conducting plate with an intervening dielectric layer.

9. A quadrature modulator according to claim 8 wherein said conducting plate is connected to ground through a resistance so as to form a notch in the filter frequency response.

10. A quadrature modulator according to claim 8 wherein said conducting plate of one RC line is connected through a resistance to said conducting plate of another RC line.

11. A quadrature modulator according to claim 9 wherein a number of said frequency notches are formed by a corresponding number of RC lines having resistances connected between ground and respective conducting plates.

12. A quadrature modulator according to claim 8 wherein an effective product of a total resistance with a total distributed capacitance of at least one of said distributed RC lines can be adjusted to a desired value after formation of said distributed RC lines.

13. A quadrature modulator according to claim 9 wherein an effective product of a total resistance with a total distributed capacitance of at least one of said distributed RC lines can be adjusted to set a notch frequency to a desired value after formation of said distributed RC lines.

14. A quadrature modulator according to claim 8 wherein at least one of said distributed RC lines is tapered.

15. A quadrature modulator according to claim 14 wherein said taper is exponential.