The stand alone RI8553A receiver is typical of the extensible design utilized by all the RI receivers, if they are integrated into a multi-function TIM or part of a mmWave system. RF or microwave signals delivered to the System Receiver are fundamentally down converted to a 21.4 MHz IF frequency using the external Microwave System Local Oscillator (LO) . The IF signal can be amplitude and bandwidth controlled before measurements are made by a either a pair of synchronous quadrature detectors slaved to the stable system wide 10 MHz reference, or a true power RMS detector. The A to D converters digitizes the sampled I and Q or RMS signal components and sends the digitized data over the RI high speed data bus (RIFL III ) to the system computer.
Two Receivers in One
The Cassini has two completely different types of receiver circuits in one operational unit. To understand how the Receiver operates it is instructive to look at the Receiver Block Diagram in more detail:
Any signal coming in to the Receiver is first bandwidth limited by the IF filter. The system allows you to chose one of three filters that have the 3 dB bandwidths as shown, 4 MHz, 200KHz and 7 kHz. They have different shapes due to their design requirements. The 7 kHz IF is a "high Q" filter designed to separate a signal from another in close proximity and has an equivalent noise power bandwidth of 10 KHz. The 4 MHz Filter is designed to pass wide-band signals and reject the Receiver's LO, 21.4 MHz away. The 200 Khz filter is part of the I/Q demodulator design and is realized there.
After the IF Filter, there is a variable gain amplifier with approximately 6 dB adjustment steps up to 66 dB of gain. The signal is then presented to one of two user selectable detection circuits. The default and most widely used is the Complex, or IQ detector circuit that has a 3 dB bandwidth of approximately 200 kHz. The Noise, or RMS detector has a bandwidth of 10's of MHz.
Following is a plot of the effective Receiver bandwidth with the 4 MHz IF and the Complex Detector, this shows the IQ detectors effective filter shape.
Cascaded Effective Receiver Bandwidth
The Effective Receiver Bandwidth is the cascaded bandwidth of the IF Filter and then the appropriate Receiver.
Case 1. 7 kHz IF Filter; Either Detector: In this case the narrow IF filter Dominates. Effective Bandwidth = approximately 7 kHz ( Usable to 10kHz )
Case 2. 4 MHz IF; Complex Detector: In this case the Complex Detector's video bandwidth is the limiting factor. Effective Bandwidth = 200 kHz
Case 3. 4 MHz IF; RMS Detector: In this case the 4 MHz IF Filter is the limiting Factor. Effective Bandwidth = 4 MHz (3dB)
Receiver Noise Floor
1) The Noise Floor of the Receiver/Test Head combination ( in direct receive mode with 0 Rec Attn) is typically approx -155 dBm/Hz
2) The Noise Floor of the Receiver/Test Head combination ( in S-Parameter receive mode with 0 Rec Attn) is typically approx -130 dBm/Hz
3) The Noise Floor of the Receiver directly in low frequency mode is typically approx -120 dBm/Hz
CASSINI SYSTEM BLOCK DIAGRAM (TYPICAL 2 SOURCE RI7100A type configuration)
The Cassini System Block Diagram document contains the full size image as a PDF.
Please reference the CASSINI System Block Diagram in the Appendix.