Abstract:
Apparatus and methods for high voltage amplification with low noise are provided. In one implementation, a high voltage low noise amplification apparatus includes a low noise broadband amplification circuit configured to amplify a first component of an input signal, the first component comprising a first subset of frequencies; an output isolator configured to create an isolated signal, the isolated signal being the input signal referenced against a broadband output of the low noise broadband amplification circuit; a low frequency amplification circuit configured to amplify a second component of the signal, the second component comprising a second subset of frequencies, wherein the second subset of frequencies is lower than the first subset; and a combination circuit configured to combine the broadband output with a low frequency output of the low frequency amplification circuit.

Description:
BACKGROUND 
       [0001]    Some electrical applications require high voltage ranges to operate correctly. For example, applications that drive piezoelectric actuators use precise high voltages to accurately control the movement of the piezoelectric actuators. However, noise in the control signal of the piezoelectric actuator can render the actuator inoperable for an intended purpose. To achieve the high voltages needed in applications that need a high voltage, low noise signal, a small voltage signal may be amplified to provide a voltage signal in the hundreds of volts. However, the breakdown voltage of typical active devices limits the output voltage range of low noise amplifiers. Further, other methods of amplification develop too much noise and can render the application inoperable. For example, an AC signal can be rectified and stepped up to provide a high voltage. However, a high voltage signal produced through rectification is typically too noisy to provide a precise high voltage to accurately drive applications like a piezoelectric actuator. 
       SUMMARY 
       [0002]    Apparatus and methods for high voltage amplification with low noise are provided. In one implementation, a high voltage low noise amplification apparatus includes a low noise broadband amplification circuit configured to amplify a first component of an input signal, the first component comprising a first subset of frequencies; an output isolator configured to create an isolated signal, the isolated signal being the input signal referenced against a broadband output of the low noise broadband amplification circuit; a low frequency amplification circuit configured to amplify a second component of the signal, the second component comprising a second subset of frequencies, wherein the second subset of frequencies is lower than the first subset; and a combination circuit configured to combine the broadband output with a low frequency output of the low frequency amplification circuit. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0003]    Understanding that the drawings depict only exemplary embodiments and are not therefore to be considered limiting in scope, the exemplary embodiments will be described with additional specificity and detail through the use of the accompanying drawings, in which: 
           [0004]      FIG. 1  is a block diagram of one embodiment of an apparatus for providing high voltage amplification with a low noise programmable output offset. 
           [0005]      FIG. 2  is a block diagram illustrating one embodiment of a schematic of an apparatus for providing high voltage amplification with a low noise programmable output offset. 
           [0006]      FIG. 3  is a block diagram illustrating one embodiment of a schematic of an apparatus driving a piezoelectric actuator. 
           [0007]      FIG. 4  is a flow diagram of one embodiment of a method for producing a high voltage low noise signal. 
       
    
    
       [0008]    In accordance with common practice, the various described features are not drawn to scale but are drawn to emphasize specific features relevant to the exemplary embodiments. 
       DETAILED DESCRIPTION 
       [0009]    In the following detailed description, references are made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific illustrative embodiments. However, it is to be understood that other embodiments may be utilized and that logical, mechanical, and electrical changes may be made. Furthermore, the method presented in the drawing figures and the specification is not to be construed as limiting the order in which the individual acts may be performed. The following detailed description is, therefore, not to be taken in a limiting sense. 
         [0010]      FIG. 1  is a block diagram of an amplification apparatus  100  for providing high voltage amplification with a low noise programmable output offset. Amplification apparatus  100  receives an input signal  102 , which provides an input voltage to amplification apparatus  100 . In some implementations, input signal  102  is a control voltage that connects amplification apparatus  100  to a loop. In some implementations, amplification apparatus  100  receives input signal  102  and amplifies it to provide a high voltage for further connected devices. For example, input signal  102  provides an input voltage between  0  and  10  volts. Amplification apparatus  100  amplifies the input voltage to provide an output signal  110  with a voltage of several hundred volts to drive a high voltage application. The term “high voltage,” as used herein, refers to a voltage needed to drive an application. Further, when amplification apparatus  100  amplifies input signal  102 , output signal  110  has low noise. The term “low noise,” as used herein, refers to noise in a signal does not affect the operation of the high voltage application. 
         [0011]    To produce output signal  110 , which has a low noise and high voltage, amplification apparatus  100  isolates output signal  110  from input signal  102 . To isolate the output signal  110 , input signal  102  is received at both an output isolator  112  and a low noise broadband amplification circuit  106 . Low noise broadband amplification circuit  106  receives input signal  102  and derives a high frequency component of input signal  102 , the high frequency component includes the components of input signal  102  that are greater than a threshold frequency. For example, the threshold frequency can be one Hz. To acquire the high frequency component of input signal  102 , input signal  102  passes through a high pass filter in low noise broadband amplification circuit. When low noise broadband amplification circuit  106  isolates the high frequency component of input signal  102 , the high frequency component is amplified such that the signal transmitted from low noise broadband amplification circuit  106  is an amplified high frequency signal with a low noise. 
         [0012]    Output isolator  112  isolates input signal  102  from output signal  110  by receiving the input signal  102 , which is referenced against ground and transmitting a re-referenced signal that is the input signal re-referenced against the low noise high frequency signal transmitted from low noise broadband amplification circuit  106 . By re-referencing the input signal  102  to the low noise high frequency signal rather than to a common ground or chassis ground, the output signal  110  is isolated from noise that can exist in the common or chassis ground, which provides the original reference voltage for input signal  102 . Further, by re-referencing the input signal  102  against the low noise high frequency signal transmitted from low noise broadband amplification circuit  106 , the output signal  110  is referenced against a voltage signal that has low noise. 
         [0013]    As amplification apparatus  100  amplifies the high frequency component of input signal  102  by passing the input signal  102  through low noise broadband amplification circuit  106 , amplification apparatus  100  also amplifies the low frequency component of input signal  102 , the low frequency component including the component of input signal  102  that is less than a threshold frequency. To amplify the low frequency component of input signal  102 , amplification apparatus  100  sends the re-referenced signal that is output from output isolator  120  through a low frequency amplification circuit  104 . Low frequency amplification circuit  104  isolates the low frequency component of the re-referenced signal by filtering out the high frequency component of the re-referenced signal. When the low frequency component is isolated, low frequency amplification circuit  104  amplifies the low frequency component to a high voltage. Further, to keep noise from affecting the signal, the amplified low frequency component is also referenced against the voltage of the low noise high frequency signal. When the low frequency component is amplified, the isolated signal is low pass filtered, such that noise components greater than the threshold frequency fail to affect applications driven by the high voltage of the low frequency component. As such low frequency amplification circuit  104  outputs a low frequency signal with approximately no noise. 
         [0014]    When amplification apparatus  100  has isolated and amplified the high frequency component and the low frequency component, amplification apparatus  100  sends both the low noise low frequency signal, transmitted from low frequency amplification circuit  104 , and the low noise high frequency signal, transmitted from low noise broadband amplification circuit  106 , to a combination circuit  108 . Combination circuit  108  combines both the low noise high frequency signal and the low noise low frequency signal to form output signal  110 . Therefore output signal  110  is a low noise amplified signal having both the high and low frequency components of input signal  102 . 
         [0015]    Amplification apparatus  100  produces the low noise high voltage signal by splitting input signal  102  into a low frequency component and a high frequency component and electrically isolating the output signal  110  from the input signal  102 . By splitting the signal, amplification apparatus  100  uses circuitry in low frequency amplification circuit  104  that is designed to amplify low frequencies without unduly increasing the noise. Likewise, amplification apparatus  100  uses circuitry in broadband amplification circuit  106  that is designed to amplify high frequencies without increasing the noise. With the two amplified components, combination circuit  108  combines the two amplified signals into output signal  110 . By combining the low noise amplified low frequency component and high frequency component, output signal  110  is a low noise, high voltage signal. 
         [0016]      FIG. 2  is a block diagram illustrating a schematic of an amplification apparatus  200  for providing high voltage amplification with a low noise programmable output offset. Amplification apparatus  200  receives an input signal  202 . Input signal  202  is substantially similar to input signal  102  as described in connection with  FIG. 1 . Specifically, input signal  202  has a high frequency component and a low frequency component. As amplification apparatus  200  receives input signal  202 , amplification apparatus separates the high frequency and low frequency components of input signal  202  for separate amplification of both the low frequency and high frequency components to create an output signal  216  that represents an amplified input signal  202 . Further, amplification apparatus  200  electrically isolates the output signal  216  from input signal  202  and other sources of noise to prevent noise from impacting the ability of the output signal  216  to drive connected devices. 
         [0017]    To amplify the high frequency component, input signal  202  is received by a high pass filter  204 . High pass filter  204  is configured to allow high frequency components of input signal  202  to pass through while removing the low frequency component of input signal  202 . For example, high pass filter  204  filters out signal frequencies that are less than one hertz. High pass filter  204  can be a LRC filter and the like. After high pass filter  204  removes the low frequency component from input signal  202 , high pass filter sends the high frequency component to a broadband high voltage amplifier  206 . Broadband high voltage amplifier  206  amplifies the high frequency component. In some implementations, Broadband high voltage amplifier  206  is a low noise amplifier designed to amplify a wide range of high frequency electrical signals. Broadband high voltage amplifier  206  introduces relatively little noise into the amplified high frequency component when compared to the voltage gain as broadband high voltage amplifier  206  operates through a linear operative range. 
         [0018]    To electrically isolate output signal  216  from input signal  202 , Amplification apparatus  202  also receives input signal  202  on optical isolator  208 . Optical isolator  208  is an electronic device that transfers electrical signals by utilizing light waves to provide coupling with electrical isolation between the input and output of optical isolator  208 . Optical isolator  208  prevents high voltages and rapidly changing voltages from passing from its input to the output. Further, input signal  202 , as received by optical isolator  208  is referenced against a common ground or chassis ground. When optical isolator  208  transfers the electrical signal to the output of optical isolator  208 , the optical isolator  208  references the output of optical isolator  208  against a voltage source other than the common ground or chassis ground used as a reference for the input of optical isolator  208 . By referencing the output of the optical isolator to a different ground than the ground used as a reference for the input signal, the output of optical isolator  208  is electrically isolated from input signal  202 . In some implementations, the output of optical isolator  208  is referenced against the low noise high frequency signal from broadband high voltage amplifier  206 . By using the low noise high frequency signal from broadband high voltage amplifier  206  as a voltage reference for the output of optical isolator  208 , a source with known low noise is used as a reference and noise from ground is prevented from affecting the output of optical isolator  208 . 
         [0019]    Amplification apparatus  200  uses the output of optical isolator  208  as an input for a high voltage programmable power supply  210 . Further, in some implementations, high voltage programmable power supply  210  uses the low noise high frequency signal from broadband high voltage amplifier  206  as a reference voltage. Also, high voltage programmable power supply  210  receives a voltage input from voltage source  214 . Voltage source  214  is a device that provides a voltage. For example, in some embodiments, voltage source  214  is a potentiometer coupled to a positive voltage source. High voltage programmable power supply  210  adds the voltages received from optical isolater  208  with the voltage received from voltage source  214  and outputs a high voltage with a low noise. Further, high voltage programmable power supply  210  is unresponsive to rapid changes in input signals. As such, high voltage programmable power supply  210  filters out the high frequency component of the output of optical isolator  208  and isolates the low frequency component of the output of optical isolator  208 . As high voltage programmable power supply  210  filters out the high frequency component, the noise that exists in the high frequency bands also is filtered out of the signal. Therefore, high voltage programmable power supply provides a low frequency signal with approximately no noise in the upper frequencies as an output. 
         [0020]    As broadband high voltage amplifier  206  provides a low noise high frequency signal and high voltage programmable power supply  210  provides a low frequency signal with negligible noise, Amplification apparatus  200  combines the two signals to produce output signal  216 , output signal  216  being a highly amplified, low noise representation of input signal  202 . In some implementations, amplification apparatus  200  combines the low noise high frequency signal and the low noise low frequency signal through passive low pass filter  212 . Passive low pass filter  212  further filters the low noise low frequency signal and then couples it with the low noise high frequency signal. For example, passive low pass filter  212  can be a low pass RC filter. When passive low pass filter  212  is a low pass RC filter, passive low pass filter  212  further filters frequencies in the high frequency spectrum of the low noise low frequency signal and then capacitatively couples the low noise high frequency signal with the low noise low frequency signal to create output signal  216 . Therefore the output signal  216  contains both the amplified low and high frequency components of input signal  202 . 
         [0021]      FIG. 3  is a block diagram illustrating a schematic of amplification apparatus  200  driving a tuning application  300 . In some applications, tuning application  300  is tuned by a piezoelectric actuator  302 . For example, in some implementations, tuning application  300  is an optical cavity with a laser that travels between reflective surfaces. Piezoelectric actuator  302  can connect to a reflective surface and be controlled to set the distance that the laser travels within the optical cavity. By controlling the distance within the optical cavity, the amplification apparatus can drive the piezoelectric actuator  302  to set the distance between reflective surfaces in the optical cavity such that the laser resonates within the cavity. In some implementations, a high voltage signal with low noise is needed to accurately drive piezoelectric actuator  302  within an optical cavity. To determine the voltage needed, a tuning controller  304  receives a signal from tuning application  300  indicating whether piezoelectric actuator  302  is at the correct distance. Tuning controller  304  transmits a signal to amplification apparatus  200  that is a driving signal to be amplified to a sufficiently high voltage to capably drive piezoelectric actuator. Amplification apparatus  200  amplifies the voltage and drives the piezoelectric actuator  302  with the amplified voltage, where the amplified voltage is in the hundreds of volts. For example, piezoelectric actuator  302  is made from lead zirconate titanate (PZT). When piezoelectric actuator  302  is made from PZT, amplification apparatus  200  provides an output signal  216  with a magnitude in the hundreds of volts. As amplification apparatus  200  amplifies an input signal  202  received from tuning controller  304  to drive piezoelectric actuator  302 , amplification apparatus  200  also limits the amount of noise introduced into the signal. By limiting the noise added during the amplification of input signal  202 , output signal  216  provided by amplification apparatus  200  is able to accurately drive piezoelectric actuator  302  in tuning application  300 . 
         [0022]      FIG. 4  is a flow diagram of a method  400  for producing a high voltage low noise signal. At block  402 , an input signal is received. For example, an amplification circuit receives an input signal. At block  404 , a high frequency component of the input signal is isolated. For example, the amplification circuit passes the input signal through a high pass filter, the high pass filter removing a low frequency component from the input signal. At block  406 , the high frequency component is amplified to create an amplified high frequency component. For instance, the amplification circuit passes the high frequency component of the input signal through a broadband high voltage amplifier. 
         [0023]    At block  408 , a low frequency component of the isolated input signal is isolated. For example, the isolated input signal is passed through a low pass filter to remove the high frequency portion of the isolated input signal. Alternatively, the isolated input signal is passed into high voltage programmable power supply, where the high frequency portion of the isolated input signal is removed. 
         [0024]    At block  410 , the low frequency component is amplified to create an amplified low frequency component. For instance, when the isolated input signal is passed into a high voltage programmable power supply, the high voltage programmable power supply amplifies the isolated input signal by using a power supplied on another input of the high voltage programmable power supply in conjunction with the isolated input signal to create the amplified low frequency component. In another example, the low frequency component is amplified by combining the amplified low frequency component with a variable offset voltage and controlling the output of a high voltage power supply with the combined amplified low frequency component and variable offset voltage. 
         [0025]    At block  412 , the amplified low frequency component and the amplified high frequency component are combined to create an output signal. For example, a low pass filter further filters out high frequency portions of the amplified low frequency component and capacitatively couples the amplified low frequency component with the amplified high frequency component. The amplification circuit then transmits the combined amplified low frequency component and amplified high frequency component as a low noise output signal to drive an application that requires a high voltage but low noise. 
         [0026]    Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiments shown. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.