Active current cancellation for high performance video clamps
View Patent ↗An apparatus comprising a first circuit, a second circuit and a third circuit. The first circuit may be configured to generate a video input signal having a voltage. The second circuit may have a finite input resistance configured to generate a current in response to presenting the voltage across the finite input resistance. The third circuit may be configured to cancel the current by (i) generating the current in response to presenting the voltage across a replica resistor having a resistance similar to the finite input resistance and (ii) passing the current away from the apparatus.
1. An apparatus comprising:
a first circuit configured to generate a video input signal having a voltage;
a second circuit having a finite input resistance configured to generate a first current in response to applying said voltage across said finite input resistance, and
a third circuit to (a) receive said voltage and (b) cancel said current by generating a second current having a negative value when compared with said first current, wherein said second current is generated in response to applying said voltage across a replica resistor having a resistance similar to said finite input resistance.
2. The apparatus according to claim 1 , wherein said third circuit further comprises:
a first operational amplifier to (i) duplicate said voltage generated in said first circuit and (ii) present said voltage to said replica resistor; and
one or more current sources configured to pass said current away from said apparatus.
3. The apparatus according to claim 2 , wherein said third circuit further comprises a first transistor, a second transistor and a third transistor, wherein said second transistor and said third transistor form a current mirror circuit.
4. The apparatus according to claim 3 , wherein (i) said first transistor is an N-type transistor, (ii) said second transistor is a P-type transistor and (iii) said third transistor is a P-type transistor.
5. The apparatus according to claim 2 , wherein said one or more current sources include a first current source and a second current source.
6. The apparatus according to claim 1 , wherein said first circuit further comprises a second operational amplifier, a first resistor and a second resistor.
7. The apparatus according to claim 6 , wherein said operational amplifier, said first resistor and said second resistor are implemented as an inverted operational amplifier circuit to provide linear and high bandwidth properties for said apparatus.
8. The apparatus according to claim 6 , where said second resistor is a variable resistor.
9. The apparatus according to claim 1 , further comprising:
a clamp circuit to restore a DC level of a portion of said video input signal to a predetermined value.
10. The apparatus according to claim 1 , wherein said apparatus is implemented in a system selected from the group consisting of video clamps and instrumentation amplifiers.
11. An apparatus comprising:
a first circuit configured to generate a video input signal having a voltage;
a second circuit having a finite input resistance configured to generate a first current in response to applying said voltage across said finite input resistance, and
a third circuit to (i) divide said voltage into a predetermined voltage level with a high impedance divider and (ii) cancel said current by generating a second current having a negative value when compared to said first current, in response to applying said predetermined voltage level across a replica resistor.
12. The apparatus according to claim 11 , wherein said high impedance divider comprises one or more resistors.
13. The apparatus according to claim 12 , wherein said third circuit further comprises a first operational amplifier coupled to said one or more resistors.
14. The apparatus according to claim 12 , wherein said replica resistor includes a resistance which is proportional to said finite input resistance.
15. The apparatus according to claim 13 , wherein said third circuit further comprises a first transistor, a second transistor and a third transistor, wherein said second transistor and said third transistor form a current mirror circuit.
16. The apparatus according to claim 15 , wherein (i) said first transistor is an N-type transistor, (ii) said second transistor is a P-type transistor and (iii) said third transistor is a P-type transistor.
17. The apparatus according to claim 11 , wherein said third circuit comprises one or more current sources configured to pass said current away from said apparatus.
18. The apparatus according to claim 11 , wherein said first circuit further comprises a second operational amplifier, a first resistor and a second resistor.
19. The apparatus according to claim 18 , wherein said second operational amplifier, said first resistor and said second resistor are implemented as an inverted operational amplifier circuit to provide linear and high bandwidth properties for said apparatus.
20. A method for actively canceling a current for high performance video clamps:
(A) generating a video input signal having a voltage;
(B) providing a finite input resistance to generate a first current in response to presenting said voltage across said finite input resistance;
(C) generating a second current having a negative value when compared with said first current in response to presenting said voltage across a replica resistor having a resistance similar to said finite input resistance; and
(D) canceling said current in response to performing steps (A)-(C).