Abstract:
A system can include an input signal source, a local oscillator (LO), and an intermediate frequency (IF) receiver to receive an input signal from the input signal source and an LO signal from the LO. The IF receiver can include a switch to switch between the first and second inputs to provide an output. The IF receiver can generate a calibration signal from the LO signal.

Description:
BACKGROUND 
     Various types of electronic devices, such as spectrum analyzers, usually have multiple input signals. One such input signal, which is generally referred to herein as a reference signal, is typically used to adjust for gain variations over time and temperature. However, because it is often significantly expensive to design and build an accurate and leveled source at many frequencies, the reference signal is usually a fixed source signal at a relatively low frequency such that its complexity and cost can be at least somewhat controlled. This source is typically calibrated in connection with being generated at the factory. 
     Accordingly, there remains a need for improved electronic device designs that do not require a discrete reference signal input. 
     SUMMARY 
     Embodiments of the disclosed technology generally include systems and devices in which a local oscillator (LO) input may be used as an alignment signal source. In certain embodiments, a power detector may be used to measure the power level of the LO input. A mixer may be optionally inserted into the reference signal path to allow for modulation or application of frequency offset to the calibration signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a schematic view of a first example of a system in accordance with certain embodiments of the disclosed technology. 
         FIG. 2  illustrates a schematic view of a second example of a system in accordance with certain embodiments of the disclosed technology. 
     
    
    
     DETAILED DESCRIPTION 
     In current electronic systems and devices, such as spectrum analyzers, a single reference frequency is typically used to adjust for gain changes that are consistent across all input frequencies. However, this is usually an issue with system architectures having devices in the radio frequency (RF) path that have variations in their frequency response over time, temperature, or both. 
     In certain embodiments of the disclosed technology, the local oscillator (LO) frequency of an electronic device, such as a Direct Conversion Receiver, is generally the center frequency of the incoming RF bandwidth. This LO frequency may be used as a reference signal for alignment and also to convert an incoming RF signal to baseband. That is, whereas conventional systems require a separate calibration signal in addition to the source signal, embodiments of the disclosed technology generally use the source signal for calibration. 
     In certain embodiments, a power detector may be used to measure the power level of the LO signal. Such power detector may be calibrated at the factory. Unlike current calibration methods, this architecture may advantageously provide a reference signal over the entire RF range for the device. 
     Gain may be optionally added prior to the power detector to keep the power at the detector relatively high so that it may be accurately measured. Alternatively or in addition thereto, an attenuator may be added after the power detector to reduce the signal level to near full scale of the instrument, or to some other desired calibration level. In such embodiments, the calibration signal may be injected after or ahead of the test instrument input attenuator. 
     In certain embodiments, a mixer may be optionally inserted into the reference signal path to allow for modulation or application of frequency offset to the calibration signal. 
       FIG. 1  illustrates a schematic view of a first example  100  of a system in accordance with certain embodiments of the disclosed technology. In the illustrated example  100 , a radio frequency (RF) signal from an RF input  102  may be received by an optional input RF attenuator  104  before being provided to the first input of an electrical switch  106 . 
     A local oscillator (LO) signal  110  is provided to a first mixer  108  and a second mixer  126 . The first mixer  108  may allow for application of a frequency offset of the LO signal  110  and may optionally receive a modulation input  112  for certain types of processing such as two-tone processing, for example. 
     The resulting LO signal  110  may be amplified by an optional amplifier  114  before being provided to a power splitter  116 , which may provide the signal to a calibrated power detector  120  and also to an optional LO attenuator  118  before providing the signal to the second input of the electrical switch  106 . 
     In the example, the electrical switch  106  is configured to pass the selected signal to an RF path  124 . The RF path  124  signal may pass through an optional instrument filter  122 , a preamplifier  123 , or both before being provided to the second mixer  126 , which is configured to output an intermediate frequency (IF) signal  128  that may be passed to other circuitry for further conversion, such as an analog-to-digital converter (ADC), for example. 
       FIG. 2  illustrates a schematic view of a second example  200  of a system, in this case a direct conversion (zero IF or ZIF) example, in accordance with certain embodiments of the disclosed technology. In the illustrated example  200 , an RF signal from an RF input  202  may be received by an optional input RF attenuator  204  before being provided to the first input of an electrical switch  206 . 
     An LO signal  210  may be provided to an optional first mixer  208 , which may also receive a modulation input  212 . 
     The resulting LO signal may be amplified by an optional first amplifier  214  before being provided to a power splitter  216 , which may provide output to a calibrated power detector  220  and also to an optional LO attenuator  218  before providing the signal to the second input of the electrical switch  206 . 
     In the example, the electrical switch  206  is configured to pass the selected signal to an RF path  224 . The RF path  224  signal may pass through an optional instrument preamplifier  222 , a filter  223 , or both before being provided to a quadrature (I/Q mixer  226 , which also receives the LO signal  210  for direct (I/Q conversion of the RF path  224  signal. Each of the resulting output signals  228  and  228  may be passed to other circuitry (not shown) for further processing. 
     Having described and illustrated the principles of the invention with reference to illustrated embodiments, it will be recognized that the illustrated embodiments may be modified in arrangement and detail without departing from such principles, and may be combined in any desired manner. And although the foregoing discussion has focused on particular embodiments, other configurations are contemplated. In particular, even though expressions such as “according to an embodiment of the invention” or the like are used herein, these phrases are meant to generally reference embodiment possibilities, and are not intended to limit the invention to particular embodiment configurations. As used herein, these terms may reference the same or different embodiments that are combinable into other embodiments. 
     Consequently, in view of the wide variety of permutations to the embodiments described herein, this detailed description and accompanying material is intended to be illustrative only, and should not be taken as limiting the scope of the invention. What is claimed as the invention, therefore, is all such modifications as may come within the scope and spirit of the following claims and equivalents thereto.