MODULATOR APPARATUS OPERATING AT LOW SUPPLY VOLTAGE, AND CORRESPONDING METHOD OF MODULATION

• US 20070200622A1
• Filed: 01/04/2007
• Published: 08/30/2007
• Est. Priority Date: 01/05/2006
• Status: Active Grant

• Current Assignee: STMicroelectronics International N.V. (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Cavallaro, Alberto, Chiarillo, Tiziano, Filoramo, Pietro
• Granted Patent: US 7,405,608 B2
• Time in Patent Office: Days
• US Class Current: 330/10
• CPC Class Codes: H03D 2200/0025 Gain control circuits
• CPC Class Codes: H03D 2200/0033 Current mirrors
• CPC Class Codes: H03D 2200/0084 Lowering the supply voltage and saving power
• CPC Class Codes: H03D 7/1433 using bipolar transistors H03D7/145 takes precedence
• CPC Class Codes: H03D 7/1441 using field-effect transistors H03D7/145 takes precedence
• CPC Class Codes: H03D 7/1458 Double balanced arrangements, i.e. where both input signals are differential
• CPC Class Codes: H03F 2200/513 the amplifier being made for low supply voltages
• CPC Class Codes: H03F 2203/45008 the addition of two signals being made by a resistor addition circuit for producing the common mode signal
• CPC Class Codes: H03F 2203/45028 the differential amplifier amplifying transistors are folded cascode coupled transistors
• CPC Class Codes: H03F 2203/45074 A comparator circuit compares the common mode signal to a reference before controlling the differential amplifier or related stages
• CPC Class Codes: H03F 2203/45078 the common mode signal being taken or deducted from the one or more inputs of the differential amplifier
• CPC Class Codes: H03F 2203/45082 the common mode signal being taken or deducted from the one or more outputs of the differential amplifier
• CPC Class Codes: H03F 2203/45136 One differential amplifier in IC-block form being shown
• CPC Class Codes: H03F 2203/45418 the CMCL comprising a resistor addition circuit
• CPC Class Codes: H03F 2203/45424 the CMCL comprising a comparator circuit
• CPC Class Codes: H03F 2203/45541 the IC comprising dynamic biasing means, i.e. controlled by the input signal
• CPC Class Codes: H03F 2203/45542 the IC comprising bias stabilisation means, e.g. DC level stabilisation, and temperature coefficient dependent control, e.g. by DC level shifting
• CPC Class Codes: H03F 2203/45588 the IC comprising offset compensating means
• CPC Class Codes: H03F 2203/45594 the IC comprising one or more resistors, which are not biasing resistor
• CPC Class Codes: H03F 2203/45644 the LC comprising a cross coupling circuit, e.g. comprising two cross-coupled transistors
• CPC Class Codes: H03F 2203/45652 : the LC comprising one or more further dif amp stages, either identical to the dif amp or not, in cascade
• CPC Class Codes: H03F 3/45192 : Folded cascode stages
• CPC Class Codes: H03F 3/45475 : using IC blocks as the active amplifying circuit
• CPC Class Codes: H03F 3/45632 : in differential amplifiers with FET transistors as the active amplifying circuit H03F3/4578 takes precedence

Abstract

A modulator apparatus operating at a low supply voltage, configured for receiving an input-voltage signal in base band and supplying an output-voltage signal at a given modulation frequency under control of a signal generated by a local oscillator and comprising a transconductor stage that carries out a voltage-to-current conversion of said input-voltage signal. A voltage-to-current conversion module is coupled to a current-mirror module configured for mirroring a current in a Gilbert-cell stage, which supplies an output-voltage signal under the control of said signal generated by the local oscillator. The Gilbert-cell stage further comprises an output load for carrying out a current-to-voltage conversion and supplying the output-voltage signal. Said transconductor stage further comprises a differential feedback network configured for reproducing said input-voltage signal on a differential load included in said voltage-to-current conversion module.

Claims

1. A modulator apparatus operating at a low supply voltage, configured for receiving an input-voltage signal from a base band circuit and supplying an output-voltage signal at a modulation frequency under control of a signal generated by a local oscillator, the modulator apparatus comprising:

a Gilbert-cell stage which supplies an output-voltage signal under the control of said signal generated by said local oscillator, the Gilbert-cell stage further including an output load for carrying out a current-to-voltage conversion and supplying the output-voltage signal; and

a transconductor stage having;

a voltage-to-current conversion module structured to perform a voltage-to-current conversion of said input-voltage signal and having a differential load;

a differential feedback network configured for reproducing in a proportional way said input-voltage signal on the differential load, and

a current-mirror module coupled to said voltage-to-current conversion module and configured for mirroring a current in the Gilbert-cell stage.

2. The apparatus according to claim 1 wherein said transconductor stage further comprises a common-mode feedback network configured for controlling an input of said voltage-to-current conversion module.

3. The apparatus according to claim 1 wherein said differential feedback network comprises a first differential amplifier configured for receiving said input-voltage signal through an impedance divider, outputs of said first differential amplifier being connected to said current-mirror module.

4. The apparatus according to claim 3 wherein said impedance divider is connected to said differential load.

5. The apparatus according to claim 2 wherein said common-mode feedback network comprises a second differential amplifier having inputs that receive common-mode-voltages collected from said common-mode feedback network, an output of said second differential amplifier controlling a biasing voltage of gates of common-gate transistors included in said voltage-to-current conversion module.

6. The apparatus according to claim 5 wherein said common-mode feedback network further comprises a first common-mode resistor connected to an input of said current-mirror module and a second common-mode resistor connected to an output of said current-mirror module wherein said common-mode feedback network collects said common-mode voltages on respective common-mode nodes.

7. The apparatus according to claim 1 wherein the transconductor stage and the Gilbert-cell stage are made with NMOS technology.

8. The apparatus according to claim 1 wherein the transconductor stage and the Gilbert-cell stage are included in an I/Q modulator.

9. The apparatus according to claim 1 wherein the transconductor stage and the Gilbert-cell stage are used for a procedure of conversion of signals to higher frequencies, or up-conversion.

10. The apparatus according to claim 1 wherein the transconductor stage and the Gilbert-cell stage are used for a procedure of conversion of signals to lower frequencies, or down-conversion.

11. A method of modulation operating at a low supply voltage, comprising:

receiving an input-voltage signal in base band and supplying an output-voltage signal at a modulation frequency under control of a signal generated by a local oscillator;

carrying out a voltage-to-current conversion of said input-voltage signal and an operation of mirroring of a current obtained;

carrying out a frequency conversion via a Gilbert-cell stage under the control of said signal generated by said local oscillator;

carrying out a current-to-voltage conversion and supplying the output-voltage signal; and

applying a differential feedback for reproducing in a proportional way said input-voltage signal on a differential load that controls said voltage-to-current conversion.

12. The method according to claim 11, further comprises applying a common-mode feedback for controlling said voltage-to-current conversion.

13. The method according to claim 11 wherein applying said differential feedback comprises providing a differential amplifier for receiving said input-voltage signal through an impedance division and controlling the mirroring operation.

14. The method according to claim 13 wherein applying said differential feedback comprises associating in signal relationship said impedance division and said differential load.

15. The method according to claim 12 wherein applying said common-mode feedback includes supplying inputs of a second differential amplifier with common-mode voltages collected in said common-mode feedback, and controlling via said second differential amplifier a biasing gate voltage of common-gate transistors included in a voltage-to-current conversion module.

16. The method according to claim 11 wherein applying said differential feedback comprises directly controlling a differential voltage applied to gate electrodes of transistors that carry out said mirroring operation.

17. The method according to claim 11 wherein the method of modulation is used for a procedure of conversion of signals to higher frequencies, or up-conversion.

18. The method according to claim 11 wherein the method of modulation is used for a procedure of conversion of signals to lower frequencies, or down-conversion.

19. A transconductor circuit comprising:

a current mirror circuit configured to generate a differential current signal;

a first differential amplifier operable to receive a first voltage signal and generate an output signal to control the current mirror circuit;

a voltage-to-current conversion circuit to receive a second voltage signal proportional to the first voltage signal and convert the second voltage signal to a current signal; and

a second differential amplifier operable to control the voltage-to-current conversion circuit.

20. The transconductor circuit of claim 19, further comprising a common-mode feedback circuit configured to control an input of the voltage-to-current conversion circuit.

21. The transconductor circuit of claim 20 wherein the first differential amplifier receives the first voltage signal via an impedance divider.