Modulator and method for producing a modulated signal

• US 7,778,356 B2
• Filed: 06/12/2006
• Issued: 08/17/2010
• Est. Priority Date: 06/14/2005
• Status: Active Grant

• Current Assignee: Given Imaging Limited (Medtronic Plc)
• Original Assignee: Given Imaging Limited (Medtronic Plc)
• Inventors: Bettesh, Ido
• Primary Examiner(s): Payne; David C
• Assistant Examiner(s): KASSA, ZEWDU A
• Application Number:
  US11/450,513
• Publication Number:
  US 20060280258A1
• Time in Patent Office: 1,527 Days
• Field of Search: 375/308, 375/302, 375/295, 375/242, 375/259, 375/353, 331/175, 331/182, 331/183, 331/177
• US Class Current: 375/308
• CPC Class Codes: H03C 3/095 applying frequency modulation to the loop in front of the voltage controlled oscillator
• CPC Class Codes: H03C 3/0958 applying frequency modulation by varying the characteristics of the voltage controlled oscillator
• CPC Class Codes: H04L 27/2014 in which the phase changes in a piecewise linear manner during each symbol period, e.g. minimum shift keying, fast frequency shift keying H04L27/201 takes precedence

Abstract

A modulator including a direct modulation synthesizer circuit, a reference frequency oscillator for providing an input reference signal to the direct modulation synthesizer circuit for locking a carrier frequency to a stable frequency and a pre-emphasis unit for data bits and for producing a modulating signal for direct modulation of the direct modulation synthesizer circuit, the modulating signal having data bit dependent voltage levels.

Claims

1. A modulator comprising:

a direct modulation synthesizer circuit for producing a modulated signal to be inputted to a transmitter;

a reference frequency oscillator for providing an input reference signal to the direct modulation synthesizer circuit for locking a carrier frequency to a stable frequency; and

a pre-emphasis unit for receiving data bits and for producing a modulating signal for direct modulation by the direct modulation synthesizer circuit, the modulating signal having data bit dependent voltage levels;

wherein the pre-emphasis unit is a digital-to-analog converter and wherein each voltage level of the modulating signal is a function of the bit values of a given data bit and of at least one data bit preceding the given data bit;

wherein the modulating signal has at least four voltage levels;

wherein the at least four voltage levels are;

V0, if the given data bit is “

0” and

the preceding data bit is “

0”

;

V0−

δ

V, if the given data bit is “

0” and

the preceding data bit is “

1”

;

V1, if the given data bit is “

1” and

the preceding data bit is “

1”

; and

V1+δ

V, if the given data bit is “

1” and

the preceding data bit is “

0”

.

2. The modulator according to claim 1, wherein the modulator is a CPFSK (Continuous Phase Frequency Shift Keying)modulator.

3. The modulator according to claim 1, wherein the direct modulation synthesizer circuit comprises a voltage controlled oscillator, into which the modulating signal is inputted, a phase detector that produces a phase detector output signal by comparing the input reference signal with a local frequency signal outputted from a feedback frequency divider connected to the voltage controlled oscillator, a charge pump that receives the phase detector output signal and that has an output signal that is inputted into a loop filter that produces a filtered signal that is inputted into the voltage controlled oscillator together with the modulating signal.

4. The modulator according to claim 1, wherein the modulator is located in an in-vivo sensing device.

5. An in-vivo sensing device comprising a modulator, the modulator comprising:

a direct modulation synthesizer circuit for producing a modulated signal to be;

inputted to a transmitter;

a reference frequency oscillator for providing an input reference signal to the direct modulation synthesizer circuit for locking a carrier frequency to a stable frequency;

a pre-emphasis unit for receiving data bits and for producing a modulating signal for direct modulation of the direct modulation synthesizer circuit, the modulating signal having data bit dependent voltage levels;

wherein the pre-emphasis unit is a digital-to-analog converter and wherein each voltage level of the modulating signal is a function of the bit values of a given data bit and at least of the data bit preceding the given data bit;

wherein the modulating signal has at least four voltage levels;

wherein the at least four voltage levels are;

VO, if the given data bit is “

0” and

the preceding data bit is “

0”

;

VO −

δ

V, if the given data bit is “

0” and

the preceding data bit is “

1”

;

V1,if the given data bit is “

1” and

the preceding data bit is “

1”

; and

V1 +δ

V, if the given data bit is “

1” and

the preceding data bit is “

0”

.

6. The in-vivo sensing device according to claim 5, comprising an imager, one or more illumination sources and an optical system.

7. A method for producing a modulated signal, comprising:

providing a direct modulation synthesizer circuit;

inputting said modulating signal to the direct modulation synthesizer circuit;

outputting the modulated signal from the direct modulation synthesizer circuit; and

inputting the modulated signal to a transmitter;

wherein the modulating signal has at least four voltage levels;

wherein the at least four voltage levels are;

VO, if the given data bit is “

0” and

the preceding data bit is “

0”

;

VO −

δ

V, if the given data bit is “

0” and

the preceding data bit is “

1”

;

V1,if the given data bit is “

1” and

the preceding data bit is “

1”

; and

V1 +δ

V, if the given data bit is “

1” and

the preceding data bit is “

0”

;

where V1 and VO are standard bit-voltage levels and V1 is greater that VO, and δ

V is apositive voltage enhancement value by which the standard bit- voltage levels are altered by the pre-emphasis unit.

8. The method according to claim 7, wherein the modulator is a CPFSK (Continuous Phase Frequency Shift Keying) modulator.

9. The method according to claim 7, wherein the direct modulation synthesizer circuit comprises a voltage controlled oscillator, into which the modulating signal is inputted, a phase detector that produces a phase detector output signal by comparing the input reference signal with a local frequency signal outputted from a feedback frequency divider connected to the voltage controlled oscillator, a charge pump that receives the phase detector output signal and that has an output signal that is inputted into a loop filter that produces a filtered signal that is inputted into the voltage controlled oscillator together with the modulating signal.

10. A method for producing a modulated signal, comprising:

providing a direct modulation synthesizer circuit;

inputting a reference signal having a given frequency to the direct modulation synthesizer circuit for locking a carrier frequency to a stable frequency;

reaching a phase difference of ±

π

/2 for every symbol of a signal using a low pass filter of at least order two with damping factor having a value of less than one to produce a modulating signal;

inputting said modulating signal to the direct modulation synthesizer circuit;

wherein the modulating signal has at least four voltage levels;

wherein the at least four voltage levels are;

VO, if the given data bit is “

0” and

the preceding data bit is “

0”

;

VO −

δ

V, if the given data bit is “

0” and

the preceding data bit is “

1”

;

V1,if the given data bit is “

1” and

the preceding data bit is “

1”

; and

V1 +δ

V, if the given data bit is “

1” and

the preceding data bit is “

0”

.

11. The method according to claim 10, wherein the modulating signal outputted from the low pass filter to the direct modulation synthesizer circuit has two voltage levels.

12. The method according to claim 11, wherein the modulating signal has an overshoot if a given data bit is 1 and the data bit preceding the given data bit is 0;

and has undershoot if the given data bit is 0 and the data bit preceding the given data bit is 1.

13. The method according to claim 10, wherein the modulator is a CPFSK (Continuous Phase Frequency Shift Keying) modulator.

14. The method according to claim 10, wherein the direct modulation synthesizer circuit comprises:

a voltage controlled oscillator, into which the modulating signal is inputted, said voltage controlled oscillator to produce an output signal;

a feedback frequency divider to receive said output signal and to output a local frequency signal;

a phase detector to produce a phase detector output signal by comparing said input reference signal with said local frequency signal;

a charge pump to receive said phase detector output signal; and

a loop filter to receive said charge pump output signal and to produce a filtered signal;

wherein said filtered signal is to be inputted into said voltage controlled oscillator together with said modulating signal.