Wideband IQ modulator with RC/CR automatic quadrature network

• US 5,694,093 A
• Filed: 11/07/1995
• Issued: 12/02/1997
• Est. Priority Date: 09/22/1993
• Status: Expired due to Fees

• Current Assignee: Agilent Technologies, Inc.
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Teetzel, Andrew M., DaSilva, Marcus K.
• Primary Examiner(s): Grimm, Siegfried H.
• Application Number:
  US08/550,546
• Time in Patent Office: 756 Days
• Field of Search: 332/103, 332/104, 332/105, 332/108, 332/119, 332/151, 332/152, 375/261, 375/281, 375/298, 455/102
• US Class Current: 332/103
• CPC Class Codes: H03C 1/02 Details
• CPC Class Codes: H03C 1/52 Modulators in which carrier or one sideband is wholly or partially suppressed H03C1/28 - H03C1/34, H03C1/46, H03C1/48 take precedence
• CPC Class Codes: H03C 1/60 with one sideband wholly or partially suppressed
• CPC Class Codes: H03C 2200/0016 Pre-emphasis or de-emphasis circuits
• CPC Class Codes: H03C 2200/0058 Quadrature arrangements
• CPC Class Codes: H03C 3/00 Angle modulation H03C5/00, H03C7/00 take precedence
• CPC Class Codes: H03C 3/40 using two signal paths the outputs of which have a predetermined phase difference and at least one output being amplitude-modulated
• CPC Class Codes: H03C 5/00 Amplitude modulation and angle modulation produced simultaneously or at will by the same modulating signal H03C7/00 takes precedence
• CPC Class Codes: H03D 1/2245 using two quadrature channels H03D1/2209 takes precedence
• CPC Class Codes: H03D 3/007 by converting the oscillations into two quadrature related signals H03D3/245 takes precedence
• CPC Class Codes: H03H 11/16 Networks for phase shifting
• CPC Class Codes: H03H 11/18 Two-port phase shifters providing a predetermined phase shift, e.g. "all-pass" filters
• CPC Class Codes: H03H 11/22 providing two or more phase shifted output signals, e.g. n-phase output

Abstract

An IQ modulator incorporates a quadrature network that is responsive to a frequency dependent control signal and that has in-phase and quadrature signals that are of equal amplitude and in exact quadrature over a wide range of applied frequencies. The quadrature network includes RC and CR phase shifters whose C'"'"'s are fixed capacitors of equal value and whose R'"'"'s are made equal to each other and to the capacitive reactance of the C'"'"'s by the action of the frequency dependent control signal. The R'"'"'s may be FET'"'"'s. The frequency dependent control signal may be generated without express knowledge of the applied frequency by a servo loop that nulls out the amplitude difference between the in-phase and quadrature outputs from the quadrature network; it may also be generated from a look-up table as an express function of frequency. The frequency dependent control signal is split into separate instances that are applied to each R, and an offset may be introduced therebetween to provide extreme precision. The offset may be fixed or programmatically controlled as a function of frequency. Varactors may be used to provide variable C'"'"'s in cooperation with fixed R'"'"'s. The entire circuit may be fabricated as a GaAs IC for use in the frequency range of 200 MHz to 3GHz.

Claims

1. A modulator comprising:

a quadrature circuit having a signal input that receives an input signal to be modulated and having first and second quadrature outputs at which respectively appear first and second quadrature signals of the same frequency as the input signal but which are in quadrature with each other, the quadrature circuit also having first and second control inputs that respectively receive first and second control signals, the quadrature circuit responsive to the first control signal by producing corresponding alterations in the amplitude of the first quadrature signal and to the second control signal by producing corresponding alterations in the amplitude of the second quadrature signal;

first and second amplitude detectors respectively coupled to the first and second quadrature outputs and producing respective first and second amplitude level signals;

a difference amplifier having inputs coupled to the first and second amplitude level signals and having a difference output;

an offset circuit coupled to the difference output and that produces the first and second control signals, the amplitude of the first control signal equal to that of the difference signal increased by a selected amount and the amplitude of the second control signal equal to that of the difference signal decreased by the selected amount;

a first multiplier having an input coupled to the first quadrature signal and another input receiving a first component of a pair of signals representing program information to be modulated onto the input signal, and producing therefrom a first multiplier output signal;

a second multiplier having an input coupled to the second quadrature signal and another input receiving the remaining second component of the pair of signals representing program information, and producing therefrom a second multiplier output signal; and

a summer having first and second inputs respectively coupled to the first and second multiplier output signals and having an output at which appears the modulated input signal.

2. A modulator as in claim 1 wherein the first and second multipliers are ring mixers comprised of FET'"'"'s.

3. A modulator as in claim 2 wherein the FET'"'"'s comprising the ring mixers are unbiased.

4. A modulator as in claim 1 wherein the first and second multipliers comprise double balanced mixers.

5. A modulator as in claim 1 wherein the modulator is constructed as an integrated circuit.

6. A modulator as in claim 5 wherein the integrated circuit is of GaAs.