A buffer circuit comprised of two matched stages is provided. The first stage develops a replica voltage that is used in the second stage as the input to a wide-band amplifier. The combination of the two feedback loops in the circuit result in improved linearity. The first amplifier dominates for moderate frequencies while the second amplifier takes over for high frequencies.
1. A buffer circuit, comprising:
a first stage comprising a first amplifier and at least one device;
a second stage comprising a second amplifier and at least two devices;
wherein said second stage further comprises an open loop formed between at least one of said at least two devices and the second amplifier,
wherein a negative input of the first amplifier is essentially directly connected to a negative input of the second amplifier; wherein control terminals of said at least one device and said at least one of said at least two devices are connected.
2. The circuit of claim 1 , wherein the first stage further comprises a closed loop.
3. A buffer circuit, comprising:
a first stage comprising a first amplifier and at least one device;
a second stage comprising a second amplifier and at least two devices;
wherein said second stage further comprises an open loop formed between at least one of said at least two devices and the second amplifier,
wherein a negative input of the first amplifier is essentially directly connected to a negative input of the second amplifier,
wherein at least one of said devices comprises a transistor.
4. The circuit of claim 3 , wherein at least one of said devices comprises a field effect transistor.
5. The circuit of claim 3 , wherein at least one of said devices comprises a metal oxide semiconductor field effect transistor (MOSFET).
6. The circuit of claim 3 , wherein at least one of said devices comprises a bipolar transistor.
7. The circuit of claim 1 , wherein said first amplifier is configured to receive an input voltage.
8. The circuit of claim 1 , wherein said first amplifier is configured to receive a current.
9. The circuit of claim 1 , wherein the circuit is configured to provide an output voltage.
10. The circuit of claim 1 , wherein the first amplifier includes a negative feedback loop providing a negative feedback.
11. The circuit of claim 1 , wherein a supply voltage is connected to at least one of the devices.
12. A buffer circuit, comprising:
first amplifying means for receiving an input signal;
first transistor means for receiving an input from a first amplifier and sending an output to the first amplifier;
second transistor means for receiving an input from the first amplifier;
third transistor means for receiving an input from a second amplifier; and
outputting means for receiving an input from the second transistor means and an input from the second amplifier and outputting an output signal, wherein said output signal has low impedance.
13. The circuit of claim 12 , wherein said first amplifying means receives a voltage signal as the input signal.
14. The circuit of claim 12 , wherein said first amplifying means receives a current as the input signal.
15. A method of operating a buffer circuit, comprising the steps of:
receiving an input signal at a first stage, said first stage comprising a first amplifier and a first device;
sending a signal from the first amplifier to the first device;
feeding back a signal from said first device to said first amplifier;
sending a signal from said first stage to a second stage, said second stage comprising an open loop;
outputting, at the second stage, an output signal with low impedance; wherein a negative input of the first stage is essentially directly connected to a negative input of the second stage.
16. The method of claim 15 , wherein said step of receiving an input signal at a first stage further comprises receiving a voltage signal at a first amplifier.
17. The method of claim 16 , wherein said step of receiving an input signal further comprises converting the voltage signal into a current.
18. The circuit of claim 1 , wherein the negative input of the first amplifier is essentially directly connected to the negative input of the second amplifier by a resistor pair.