Wide linear range peak detector
A wide linear range peak detector including first and second peak detectors and a compensation circuit. The first peak detector receives an input signal and has an output providing a first peak signal approximation which approximates a peak level of the input signal. The first peak signal approximation includes a non-linear portion which is a function of the peak level of the input signal. The second peak detector also receives the input signal and has an output providing a second peak signal approximation. The compensation circuit uses the second peak signal approximation to provide a compensation signal which compensates the non-linear portion of the first peak signal approximation. In particular, the second peak signal is used to generate the compensation signal to approximate and cancel the non-linear portion.
1. A wide linear range peak detector, comprising:
a first peak detector having an input receiving an input signal and an output providing a first peak signal approximation which approximates a peak level of said input signal, wherein said first peak signal approximation comprises a non-linear portion which is a function of said peak level of said input signal;
a second peak detector having an input receiving said input signal and an output providing a second peak signal approximation; and
a compensation circuit having an input receiving said second peak signal approximation and an output which is coupled to said first peak detector, wherein said compensation circuit uses said second peak signal approximation to provide a compensation signal which compensates said non-linear portion of said first peak signal approximation;
wherein said first peak detector comprises a differential peak detector providing said first peak signal approximation with positive and negative polarity signals; and
wherein said compensation circuit has an output which is coupled to a selected one of said positive and negative polarity signals of said first peak signal approximation.
2. The wide linear range peak detector of claim 1 , wherein:
said first peak detector comprises:
a first single-ended input peak detector having an input receiving said input signal and an output providing said positive polarity signal of said first peak signal approximation; and
a first reference peak detector having an input coupled to a constant level and an output providing said negative polarity signal of said first peak signal approximation; and
wherein said second peak detector comprises:
a second single-ended input peak detector having an input receiving said input signal and an output providing a positive polarity signal of said second peak signal approximation; and
a second reference peak detector having an input coupled to said constant level and an output providing a negative polarity signal of said second peak signal approximation.
3. The wide linear range peak detector of claim 1 , wherein:
said first peak detector comprises:
a first single-ended input peak detector having an input receiving said input signal and an output providing a positive polarity signal for both of said first and second peak signal approximations; and
a first reference peak detector having an input coupled to a constant value and an output providing said negative polarity signal of said first peak signal approximation; and
wherein said second peak detector comprises:
said first single-ended input peak detector; and
a second reference peak detector having an input coupled to said constant level and an output providing a negative polarity signal of said second peak signal approximation.
4. The wide linear range peak detector of claim 1 , wherein said compensation circuit comprises:
a transconductance amplifier circuit having an input receiving said second peak signal approximation and an output; and
a square-root circuit having an input coupled to said output of said transconductance amplifier circuit and an output providing said compensation signal.
5. The wide linear range peak detector of claim 1 , wherein said compensation circuit comprises:
a differential pair circuit having a differential input receiving said second peak signal approximation and an output, wherein said differential pair circuit converts said second peak signal approximation into a first current using a second constant current; and
a translinear loop square-root circuit having an input coupled to said output of said differential pair circuit and an output providing said compensation signal, wherein said translinear loop square-root circuit multiplies said first current by a constant third current to achieve a current multiple and which performs a square-root function of said current multiple to provide said compensation signal.
6. The wide linear range peak detector of claim 5 , wherein:
said first peak detector comprises a transistor coupled to a capacitor at a negative polarity node which develops said negative polarity signal; and
wherein said output of said translinear loop square-root circuit is coupled to said negative polarity node of said first peak detector.
7. The wide linear range peak detector of claim 5 , wherein said constant second and third currents are selected to optimize compensation.
8. A wide linear range peak detector, comprising:
a first input single-ended peak detector having an input and an output, said input receiving an input signal;
a first reference single-ended peak detector having an input and an output, said input coupled to a constant voltage;
a second reference single-ended peak detector having an input and an output, said input coupled to said constant voltage;
wherein said outputs of said first input single-ended peak detector and said second reference single-ended peak detector form a first differential peak voltage approximation;
a compensation circuit having an input receiving said first differential peak voltage approximation and an output coupled to said output of said first reference single-ended peak detector; and
wherein said outputs of said first input single-ended peak detector and said first reference single-ended peak detector form a compensated differential peak voltage approximation.
9. The wide linear range peak detector of claim 8 , further comprising:
a second input single-ended peak detector having an input receiving said input signal and an output; and
wherein said outputs of said second input single-ended peak detector and said second reference single-ended peak detector form said first differential peak voltage approximation provided to said input of said compensation circuit.
10. The wide linear range peak detector of claim 8 , wherein said compensation circuit comprises:
a transconductance amplifier having a differential input receiving said first differential peak voltage approximation and an output providing a first current that is based on a constant second current; and
a square-root circuit which multiplies said first current by a constant third current to provide a current multiple and which takes the square-root of said current multiple to provide a compensation signal at said output of said compensation circuit.
11. The wide linear range peak detector of claim 8 , wherein said compensation circuit comprises:
a differential pair circuit having a differential input receiving said first differential peak voltage approximation and an output providing a first current that is based on said first differential peak voltage approximation and a constant second current; and
a translinear loop square-root circuit having an input receiving said first current which multiplies said first current by a constant third current to provide a current multiple and which takes the square-root of said current multiple to provide a compensation signal at said output of said compensation circuit.
12. The wide linear range peak detector of claim 8 , wherein said first input single-ended peak detector and said first and second reference single-ended peak detectors each comprise:
a bipolar-junction transistor having a base electrode, an emitter electrode, and a collector electrode coupled to a first voltage supply;
a bias circuit coupled to said base electrode of said bipolar-junction transistor;
a constant current sink coupled between said emitter electrode of said bipolar-junction transistor and a second voltage supply; and
a first capacitor coupled between said emitter electrode of said bipolar-junction transistor and said second voltage supply.
13. The wide linear range peak detector of claim 12 , wherein said first input single-ended peak detector and said first and second reference single-ended peak detectors each further comprise a second capacitor coupled to said base electrode of said bipolar-junction transistor.
14. The wide linear range peak detector of claim 12 , wherein said bias circuit comprises a resistor coupled between a bias voltage and said base electrode of said transistor.
15. A method of determining the peak voltage of an input signal for a wide linear range, comprising:
generating a first peak signal approximation of the input signal as a first differential approximation across a pair of capacitive output terminals, wherein the first peak signal approximation comprises a non-linear portion which is a function of the peak voltage of the input signal;
generating a second peak signal approximation;
converting the second peak signal approximation to a non-linear compensation current based on the non-linear portion of the first peak signal approximation; and
adjusting the first peak signal approximation by the compensation current to compensate for the non-linear portion by applying the compensation current to one of the pair of capacitive output terminals.
16. The method of claim 15 , wherein said converting the second peak signal approximation to a non-linear compensation current comprises:
converting the second peak signal approximation to a first current based on a constant second current;
multiplying the first current by a constant third current and providing a squared current; and
taking the square-root of the squared current.
17. A method of determining the peak voltage of an input signal for a wide linear range, comprising:
generating a first peak signal approximation of the input signal, wherein the first peak signal approximation comprises a non-linear portion which is a function of the peak voltage of the input signal;
generating a second peak signal approximation;
converting the second peak signal approximation to a compensation signal based on the non-linear portion of the first peak signal approximation; and
adjusting the first peak signal approximation by the compensation signal to compensate for the non-linear portion; and
wherein said generating the first and second peak signal approximations each comprise:
applying the input signal to the input of a first transistor-based single-ended peak detector circuit having a first capacitive output terminal; and
coupling a constant voltage to the input of a second transistor-based single-ended peak detector circuit having a second capacitor output terminal.
18. The method of claim 17 , wherein said converting and adjusting comprises:
converting the second peak signal approximation to a compensation current; and
applying the compensation current to the second capacitor output terminal.