RF Direct Conversion Receiver IC
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
VCO Negative-Resistance Amplifier
LO Divide by:
"2", "4" or "6" Modes
Analogue, Digital and Multi-mode Radio
Software Defined Radio (SDR)
Data Telemetry Modems
Constant Envelope and Linear Rx Modulation
Rx Function Compatible with CMX998 PA Linearising I/Q Modulator
Narrowband Systems: 25kHz, 12.5kHz and 6.25kHz
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.
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.