My mission, that I chose to accept, was to design the low-noise amplifier (LNA) and the local oscillator (LO) for our Bluetooth compatible receiver.  The LNA not only provides amplification, but also acts as a bandpass filter due to its LC tank circuit.  Master-slave tuning is used to keep the center frequency of the filter a constant frequency offset from the frequency of the LO.  The LO is the master and the filter is the slave following the frequency of the LO.  The frequency offset for this receiver is 120.5 MHz, this is also the first intermediate frequency (IF) of the receiver.  The filter and the LO use tank circuits that are located on-chip.  Spiral inductors and poly-poly capacitors were sized to give the proper frequency, but due to the series resistance of the inductor the Q of the tank circuit is much too low for our needs.  Negative conductance circuitry using active devices was added to improve the Q of the tank circuit, therefore decreasing the bandwidth of the filter as well as increasing its gain.  The negative conductance provides positive feedback to the tank and if a high enough amount is added oscillations will occur.  This is how the LO was designed.  The filter and oscillator are digitally tuned by adding in capacitance to the tank circuit.  The digital tuning was done in 16 MHz steps and no analog tuning was implement in this design, but will be added in future revisions.  The parameters we were trying to meet in the filter design were a nominal bandwidth of 24 MHz, a noise figure of less than 12 dB, and a voltage gain of 20 dB.  An output buffer having a differential output impedance of 2 kOhm was used for both the filter and oscillator.  Additional buffers were added to drive 50 Ohm test equipment.
 
 

Q-Enhanced LNA

Local Oscillator

Design Simulations

LNA Layout

Oscillator Layout

Layout Versus Extraction Simulations