Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H11/00—Networks using active elements
  • H03H11/02—Multiple-port networks
  • H03H11/04—Frequency selective two-port networks
  • H03H11/0422—Frequency selective two-port networks using transconductance amplifiers, e.g. gmC filters
  • H03H11/0472—Current or voltage controlled filters
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03J—TUNING RESONANT CIRCUITS; SELECTING RESONANT CIRCUITS
  • H03J2200/00—Indexing scheme relating to tuning resonant circuits and selecting resonant circuits
  • H03J2200/08—Calibration of receivers, in particular of a band pass filter

Definitions

• Figure IA is a diagram illustrating one embodiment of an offset phase- locked loop in a signal transmitter.
• Figure IB is a diagram illustrating a typical three-stage filter including integrator stages composed with transconductance (Gm) and capacitor elements.
• Figure 2 is a diagram illustrating a filter that can be reconfigured as an oscillator for the purpose of calibrating the filter.
• Figure 3 is a diagram illustrating an oscillation frequency detector.
• Figure 4 is a flowchart of a process used to calibrate a filter.
• Figure 5 is a flowchart of a process for adjusting filter components to achieve a desired oscillation frequency.
• the disclosure can be implemented in numerous ways, including as a process, an apparatus, a system, a composition of matter, a computer readable medium such as a computer readable storage medium or a computer network wherein program instructions are sent over optical or electronic communication links.
• these implementations, or any other form that the disclosure may take, may be referred to as techniques.
• the order of the steps of disclosed processes may be altered within the scope of the disclosure.
• Filter calibration is disclosed.
• the filter is reconfigured as an oscillator during calibration mode.
• Switches and/or other implementations of reconfiguring a filter are used to reconfigure the negative feedback loop of the filter to a positive feedback loop.
• the oscillation parameters are then measured to adjust the components of the filter to achieve an oscillation that corresponds to a desired filter characteristic.
• Figure IA is a diagram illustrating one embodiment of an offset phase- locked loop in a signal transmitter.
• the signal transmitter is used in a cellular communication device.
• the signal transmitter can be used in a broader set of applications requiring a highly integrated transmitter.
• the modulator 102 mixes I and Q baseband signals using the corresponding signals from the I and Q local oscillators (LO).
• the modulated signals get filtered through the harmonic reject (HR) filter 104 to be passed on to a phase-locked loop (PLL) 105.
• the incoming signal is compared to a feedback signal in the phase frequency detector (PFD) 106.
• the output of the PFD is filtered by the loop filter 108 and fed into the voltage-controlled oscillator (VCO) 110.
• VCO voltage-controlled oscillator
• the feedback path from voltage-controlled oscillator 110 includes a mixer 114 that mixes the feedback signal with a signal from a local oscillator and an HR filter 116 to filter out unwanted harmonics from the signal.
• Power amp 118 amplifies the processed signal for transmission via the antenna 120.
• the signal is amplified by a preamp before being amplified by power amp 118.
• Figure IB is a diagram illustrating a typical three-stage filter including integrator stages composed with transconductance (Gm) and capacitor elements.
• the filter shown may be used as the HR filters 104 and 116 of Figure IA.
• Other embodiments can be configured to include any number of filter stages.
• various filter stages have been cascaded to obtain a steeper filter roll-off response.
• the first stage of the filter is a single pole filter 122.
• the other filters are two stages of second-order Biquad filters 124 and 126. Biquad filter stages have been chosen for their high Q value, constant bandwidth value, and decreased sensitivity to external component variations.
• FIG. 2 is a diagram illustrating a filter that can be reconfigured as an oscillator for the purpose of calibrating the filter.
• the filter includes two second-order Biquad modules highlighted in boxes 202 and 204.
• Each Biquad module includes opamp/transconductance stage 206, opamp/transconductance stage 207, opamp/transconductance stage 208, opamp/transconductance stage 209, opamp/transconductance stage 210, opamp/transconductance stage 211, opamp/transconductance stage 212, opamp/transconductance stage 213, adjustable capacitor 214, adjustable capacitor 215, adjustable capacitor 216, adjustable capacitor 217, and may include other components including but not limited to resistors, capacitors, inductors, and power sources (not shown).
• the filter has two modes of operation: a filtering mode and a calibration/oscillation mode. In some embodiments, there may be more than two modes of operation.
• switch 218 In the filtering mode, switch 218 is closed while switch 220 and switch 222 are open, placing each Biquad in a negative feedback configuration.
• calibration mode switch 218 is open while switch 220 and switch 222 are closed.
• the Biquads are connected together in a positive feedback configuration, causing the system to oscillate.
• the criteria for filter oscillation is any third-order filter or higher (adding to a phase shift of more than 180 degrees) with an inversion in the positive feedback path. In some higher order embodiments, inversion is not required for oscillation.
• only a portion of the filter signal path is used for oscillation.
• an oscillation property is measured.
• the oscillation property measurement is used to calibrate the filter.
• a frequency detector can be connected to the filter in oscillation mode by switch 222 and can measure the frequency of the oscillation.
• the frequency measurement is related to and in certain cases can be correlated with relevant characteristics of the filter such as the filter cutoff frequency. Once a relationship between the frequency measurement and a given filter characteristic is derived either analytically or empirically, the frequency measurement can be used to adjust the filter components to achieve an oscillation frequency that corresponds to a desired characteristic of the filter.
• adjustable capacitor 214, adjustable capacitor 215, adjustable capacitor 216, and adjustable capacitor 217 are adjusted together to change the cutoff frequency (fc) of the filter. In some embodiments, the adjustable capacitors are adjusted individually to change the cutoff frequency (fc) of the filter.
• the transconductance of the filter may also be used to adjust the characteristics of the filter. A relationship between the transconductance and the frequency measurement is determined and then the oscillation frequency is adjusted to correspond to a desired transconductance.
• the oscillation signal generation may be inexpensively implemented in a filter using the switching arrangement described above without the need of external elements such as phase-locked loops to generate either calibration tones or used in a Master-Slave tuning algorithm.
• the filter in oscillation mode will induce an oscillation within fractions of microsecond. The measurement may be made on the oscillation frequency without waiting for an external PLL to settle.
• Figure 3 is a diagram illustrating an oscillation frequency detector.
• Frequency detector 300 or any other appropriate frequency detector may be connected to a filter, such as the one depicted in Figure 2.
• the incoming signal to be measured 302 is buffered through an inverter 304 to produce a square wave signal 306.
• Square wave signal 306 is fed into a counter 308.
• Counter 308 counts the number of edges in the square wave signal 306 within a prescribed time period to determine the count corresponding to the frequency of the signal. The time period may be preconfigured or dynamically configured.
• An oscillator 310 generates a reference frequency in the example shown. Similar to the incoming signal 302, this reference frequency signal is buffered by an inverter 312 to generate a reference count at counter 314.
• the ratio of the counts generated by counters 308 and 314 are used to compute an estimate of the filter oscillation frequency.
• the estimated oscillation frequency is compared to a target count found that may be stored in RAM lookup table 315.
• the target count in RAM lookup table 315 is associated with a desired count value for counter 308 which ultimately maps to the desired filter corner frequency during normal filter operation.
• the filter elements are adjusted based on the count associated with counter 308 and the target count associated with RAM lookup table 315.
• the oscillation frequency estimation and comparison may be performed a number of times using a successive approximation approach until the count value associated with a counter matches a value associated with data in RAM lookup table 315.
• the oscillator is reconfigured to a filter for normal operation by opening switches 222 and 220 while closing switch 218 of Figure 2.
• FIG. 4 is a flowchart of a process used to calibrate a filter.
• Filter calibration mode is entered at 402.
• the calibration process is invoked when the filter is powered on.
• the calibration process is invoked before every instance of a related group of data.
• the calibration process is invoked periodically.
• the calibration process is invoked by another component.
• the calibration process is invoked when the filter parameters are tuned.
• the filter is configured to oscillate at 404.
• the filter may be configured to oscillate by setting switches, relays, and/or any appropriate hardware or software component. After the reconfigured filter is oscillating, the filter components are adjusted at 406 to achieve an oscillation frequency corresponding to the desired characteristics of the filter.
• the filter components are adjusted to achieve the phase associated with the oscillation corresponding to the desired characteristics of the filter, or the current associated with the oscillation corresponding to the desired characteristics of the filter or the voltage associated with the oscillation corresponding to the desired characteristics of the filter, or any combination of the above.
• Other oscillation parameters may also be used to achieve desired filter characteristics.
• FIG. 5 is a flowchart of a process for adjusting filter components to achieve a desired oscillation frequency.
• the process of Figure 5 is used to implement 406 of Figure 4.
• the oscillation frequency of the filter is measured at 502.
• the oscillation frequency is analyzed at 504.
• Oscillation frequency analysis may include using counters to measure oscillation frequency as described above.
• oscillation frequency analysis includes comparing the oscillation frequency to a reference frequency. If the oscillation frequency is determined at 506 to be within the range of frequencies corresponding to the desired filter characteristics, a "filter calibrated" conclusion is reached at 508.
• the threshold may be configurable. In some embodiments, the threshold is configured by another device.
• the filter components are adjusted at 510 to achieve the desired frequency.
• a successive approximation method is used to adjust filter components to achieve the desired oscillation frequency.
• a formula based on current filter characteristics is used to match filter component adjustment with the desired oscillation frequency. One such formula is
• ⁇ osc is the oscillation frequency
• g m are transconductance values
• C are capacitance values of the filter shown in Figure 2.
• the formula above assumes the loop gain is linear and the ratio between the filter corner frequency and the oscillation frequency is constant.
• Other search methods may also be used to determine filter components that achieve an oscillation frequency that corresponds to a desired filter characteristic.

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• Networks Using Active Elements (AREA)
• Inductance-Capacitance Distribution Constants And Capacitance-Resistance Oscillators (AREA)

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• 2006
  • 2006-05-25 EP EP06771416A patent/EP1889358A1/de not_active Withdrawn
  • 2006-05-25 WO PCT/US2006/020636 patent/WO2006128075A1/en active Application Filing

Non-Patent Citations (1)

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