Impedance emulator

• US 6,351,137 B1
• Filed: 08/15/2000
• Issued: 02/26/2002
• Est. Priority Date: 08/15/2000
• Status: Expired due to Term

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: PulseCore Semiconductor, Inc. (ON Semiconductor Corporation)
• Inventors: Hariton, Dan Ion
• Primary Examiner(s): Tokar, Michael
• Assistant Examiner(s): Tan, Vibol
• Application Number:
  US09/637,350
• Time in Patent Office: 560 Days
• Field of Search: 326/30-32, 326/21, 326/34, 326/86, 333/22.R, 333/32, 327/538, 327/540, 327/541, 327/543, 327/63, 327/67, 327/68, 327/73
• US Class Current: 326/30
• CPC Class Codes: H03H 11/48 simulating reactances

Abstract

A method and device to emulate impedances includes a pair of impedances connected in series between a supply voltage and ground, the impedances forming a voltage divider having at its midpoint a reference voltage V_x. An OP AMP includes a positive input connected to the V_x node and the negative input connected to the output thereof in a direct feedback loop. The OP AMP output is also connected to a load impedance that is connected either to the supply voltage or ground. The unity gain OP AMP forces the output voltage thereof to follow the input voltage V_x, whereby the output voltage behaves as if it were created by a virtual impedance. By proper choice of components and values, the virtual impedance may comprise a large capacitor, and the remaining impedances may comprise resistance and small capacitance, both of which, together with the OP AMP, are easily integrated in a small die area. A transistor may be interposed between the load impedance and supply or ground to eliminate unacceptably large current flow through the OP AMP. The OP AMP may be provided with a negative gain, and the impedances may be scaled to create a virtual inductor having a predetermined value. Impedance emulator circuits may be combined so that the emulated impedance of one circuit may act as a virtual component in a further emulation circuit, whereby a wide range of component impedances values of may be replicated.

Claims

1. A impedance emulating device, including:

a voltage divider having a midpoint node at voltage V_X;

said voltage divider including at least one impedance having a reactive component;

an OP AMP having one input connected to V_X and the other input connected to the output of said OP AMP, whereby said output of said OP AMP is driven to equal V_X;

a load impedance connected at one end to said OP AMP output;

said voltage divider and said load impedance having values scaled so that V_X replicates the output of an emulated impedance of predetermined reactance and magnitude.

2. The impedance emulating device of claim 1, wherein said OP AMP has a gain of +1.

3. The impedance emulating device of claim 1, wherein said voltage divider is connected between a voltage supply and ground, and said load impedance is connected between said output of said OP AMP and said voltage supply.

4. The impedance emulating device of claim 1, wherein said voltage divider is connected between a voltage supply and ground, and said load impedance is connected between said output of said OP AMP and said ground.

5. A impedance emulating device, including:

a voltage divider having a midpoint node at voltage V_X;

an OP AMP having one input connected to V_X and an output connected to the gate of a transistor, the other input of said OP AMP connected to the source/drain circuit of said transistor, whereby said output of said OP AMP is driven to equal V_X;

a load impedance connected at one end to said other input of said OP AMP and said source/drain circuit of said transistor, whereby said source/drain circuit provides a current path to said load impedance;

said voltage divider and said load impedance having values scaled so that V_X replicates the output of an emulated impedance of predetermined reactance to and magnitude.

6. The impedance emulating device of claim 5, wherein said OP AMP has a gain of +1.

7. The impedance emulating device of claim 5, wherein said voltage divider is connected between a voltage supply and ground, and said load impedance is connected between said source/drain circuit of said transistor and said voltage supply.

8. The impedance emulating device of claim 5, wherein said voltage divider is connected between a voltage supply and ground, and said load impedance is connected between said source/drain circuit of said transistor and said ground.

9. The impedance emulating device of claim 5, wherein said voltage divider includes impedances KZ_a and KZ_b connected in series, and said load impedance includes an impedance KZ_a/K−

1, K being a numerical constant.

10. The impedance emulating device of claim 5, wherein said voltage divider includes impedances KZ_a and KZ_b connected in series, and said load impedance includes an impedance KZ_b/K−

1, K being a numerical constant.

11. The impedance emulating device of claim 5, wherein said voltage divider includes impedances KZ_a/K−

1 and KZ_b/K−

1 connected in series, and said load impedance includes an impedance KZ_a, K being a numerical constant.

12. The impedance emulating device of claim 5, wherein said voltage divider includes impedances KZ_a/K−

1 and KZ_b/K−

1 connected in series, and said load impedance includes an impedance KZ_b, K being a numerical constant.

13. The impedance emulating device of claim 5, wherein the positive input of said OP AMP is connected to V_X and the negative input of said OP AMP is connected to said source/drain circuit of said transistor.

14. A impedance emulating device, including:

a voltage divider connected between a voltage supply and ground and having a midpoint node at voltage V_X;

an amplifier having an input connected to V_X and an output V_y;

a load impedance connected between V_y and said voltage supply;

said voltage divider and said load impedance having values scaled so that V_Y replicates the output of an emulated impedance of predetermined reactance and magnitude.

15. The impedance emulating device of claim 14, wherein said amplifier has a negative gain.

16. An impedance emulating device, including:

a voltage divider having a midpoint node at voltage V_X;

an OP AMP having one input connected to V_X and the other input connected to the output of said OP AMP, whereby said output of said OP AMP is driven to equal V_X;

a load impedance connected at one end to said OP AMP output;

said voltage divider and said load impedance heaving values scaled so that V_X replicates the output of an emulated impedance of predetermined reactance and magnitude;

said voltage divider including impedances KZ_a and KZ_b connected in series, and said load impedance including an impedance KZ_a/K−

1, K being a numerical constant.

17. An impedance emulating device, including:

a voltage divider having a midpoint node at voltage V_X;

an OP AMP having one input connected to V_X and the other input connected to the output of said OP AMP, whereby said output of said OP AMP is driven to equal V_X;

a load impedance connected at one end to said OP AMP output;

said voltage divider and said load impedance having values scaled so that V_X replicates the output of an emulated impedance of predetermined reactance and magnitude;

said voltage divider including impedances KZ_a and KZ_b connected in series, and said load impedance including an impedance KZ_b/K−

1, K being a numerical constant.

18. An impedance emulating device, including:

a voltage divider having a midpoint node at voltage V_X;

an OP AMP having one input connected to V_X and the other input connected to the output of said OP AMP, whereby said output of said OP AMP is driven to equal V_X;

a load impedance connected at one end to said OP AMP output;

said voltage divider and said load impedance having values scaled so that V_X replicates the output of an emulated impedance of predetermined reactance and magnitude;

said voltage divider including, impedances KZ_a/K−

1 and KZ_b/K−

1 connected in series, and said load impedance including an impedance KZ_a, K being a numerical constant.

19. An impedance emulating device, including:

a voltage divider having a midpoint node at voltage V_X;

an OP AMP having one input connected to V_X and the other input connected to the output of said OP AMP, whereby said output of said OP AMP is driven to equal V_X;

a load impedance connected at one end to said OP AMP output;

said voltage divider and said load impedance having values scaled so that V_X replicates the output of an emulated impedance of predetermined reactance and magnitude;

said voltage divider including impedances KZ_a/K−

1 and KZ_b/K−

1 connected in series, and said load impedance including an impedance KZ_b, K being a numerical constant.

20. An impedance emulating device, including:

a voltage divider having a midpoint node at voltage V_X;

an OP AMP having one input connected to V_X and the other input connected to the output of said OP AMP, whereby said output of said OP AMP is driven to equal V_X;

a load impedance connected at one end to said OP AMP output;

said voltage divider and said load impedance having values scaled so that V_X replicates the output of an emulated impedance of predetermined reactance and magnitude;

the positive input of said OP AMP being, connected to V_X and the negative input of said OP AMP being connected to the output of said OP AMP.

21. A impedance emulating device, including:

a voltage divider connected between a voltage Supply and ground and having a midpoint node at voltage V_X;

an amplifier having an input connected to V_X and an output V_Y;

a load impedance connected between V_Y and said voltage supply;

said voltage divider and said load impedance having values scaled so that V_Y replicates the output of an emulated impedance of predetermined reactance and magnitude;

said voltage divider includes impedances R₁ and C₁ connected in series between said voltage supply and ground, said amplifier has a gain of −

N, and said emulated impedance has a resistance value R₄;

$R_4=\frac{1}{N/R_2-1/R_1}$

22. The impedance emulating device of claim 21, wherein said emulated impedance has an inductance value L₄:

23. The impedance emulating device of claim 21, further including a further impedance emulating device for creating said impedance C₁.

24. In an integrated circuit construction, a method for emulating a large reactive impedance, comprising the steps of:

providing a voltage divider comprised of at least one impedance having a relative component, said voltage divider having a midpoint node at voltage V_X;

connecting one input of an OP AMP to V_X and the other input connected to the output of said OP AMP, whereby said output of said OP AMP is driven to equal V_X;

connecting a load impedance at one end to said OP AMP output;

said voltage divider and said load impedance having values scaled so that V_X replicates the output of an emulated impedance of predetermined reactance and magnitude.

25. The method of claim 24, wherein said emulated impedance includes an inductive component.