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RF Direct Conversion Receiver IC

CMX994


Features:

Direct Conversion Receiver:

  • Direct Conversion Eliminates Image Responses
  • LNA with Gain Control
  • 100MHz to 940MHz I/Q Demodulator
  • Extended operation down to 50MHz
  • Precise Filtering with Bandwidth Setting and 1:2:4 Bandwidth Modes

Local Oscillator:

  • LO Synthesiser
  • VCO Negative-Resistance Amplifier
  • LO Divide by:
    "2", "4" or "6" Modes

Applications:

  • Analogue, Digital and Multi-mode Radio
  • Software Defined Radio (SDR)
  • Data Telemetry Modems
  • Satellite Communications
  • Constant Envelope and Linear Rx Modulation
  • Rx Function Compatible with CMX998 PA Linearising I/Q Modulator
  • Narrowband Systems: 25kHz, 12.5kHz and 6.25kHz

Supply Requirement:

  • 3.0 to 3.6 V

The CMX994 is a direct conversion receiver IC. The receiver is fully integrated with a broadband Low Noise Amplifier (LNA) preceding the down-converter section and a high dynamic-range I/Q demodulator.

The receiver baseband section includes amplifiers and precise baseband filter stages. High-linearity down-converting mixers are immediately followed by a baseband filter stage.

The first stage of filtering is designed to remove off-channel blocking signals prior to baseband amplification. Following the filters, gain is applied via an on-chip variable gain amplifier.

LO generation is provided by an integer-N PLL and VCO negative-resistance amplifier suitable for VHF operation; an external LO may be used for other bands. LO dividers are provided for flexible multi-band operation.

The receiver I/Q chain includes the facility to correct for inherent dc offsets in the hardware. This process is intended to optimise the dynamic range of the system and must be controlled by the microprocessor or DSP that processes the I/Q signals from the IC.

Until recently, most radios have used the superheterodyne (superhet) receiver architecture, however enhancements in semiconductor technology have enabled the integration of DCRx, making it now the technology of choice.

Block Image

CMX994

Design Support Information

 
Frequency Estimation for a VCO using a Negative Resistance Amplifier Application Note describing how to estimate the operating frequency of VCO designs using a negative resistance amplifier. An Excel spreadsheet that automates the calculation is available below.
Excel Spreadsheet - Frequency Estimation for a VCO using a Negative Resistance Amplifier An Excel spreadsheet that calculates the operating frequency of VCO designs using a negative resistance amplifier. An Application Note describing the process is available above.
 
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