Tektronix RTX130B, Service Manual

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Theory of Operation
RTX130B QAM & VSB RF Signal Generator Service Manual
2-5
The Local Bus interface consists of U5, U6, U7, and U8. U5 is a local bus data
driver/receiver, U6 is a control signal driver/receiver, U7 is an LVDS receiver,
and U8 is an LVDS driver.
U11 (symbol clock generator) and U12 (base clock generator) are programmable
clock generators. The application software can program these clock generators
via I2C interface in the digital modulator.
U35 is a switching regulator for the internal supply voltage of the digital
modulator. It co3.3 V to +1.2 V.
U36 is a linear voltage regulator for the auxiliary supply voltage of the digital
modulator. It co3.3 V to + 2.5 V.
U14 is a cable equalizer for an ASI/SMPTE310M signal. The ASI receiver
converts an 8B/10B signal to a parallel signal.
U15 is a programmable SMPTE receiver that can be reprogrammed via the J4
connector. There are an SMPTE310M decoder and PLL controller in U15.
U18 (CY7B9234) is an ASI transmitter. It converts parallel data to 8B/10B serial
data.
U20 (MC100EL57) is an output selector. It selects one of the four input status;
low level, loop-through signal, SMPTE310M signal and ASI output.
U21 (CLC007) is a cable driver. It can drive a 75 Ω coaxial cable.
M1 is a VCO for the SMPTE310M receiver. The frequency is controlled by an
SMPTE310M input signal.
U22 (AD9857) is a quadrature digital up-converter and DAC. It consists of
digital filters, quadrature modulator, DDS (direct digital synthesis), and 14-bit
DAC. The quadrature modulator converts I/Q data to real data. The 14-bit DAC
converts the digital output from the quadrature modulator to an analog signal.
The low pass filter is connected to the output of AD9857. It is a 7th order elliptic
filter and removes Nyquist images.
Local Bus Interface
Base Clock Generator and
Symbol Clock Generator
Switching Regulator
Linear Voltage Regulator
Cable Equalizer and ASI
Receiver
SMPTE310M Receiver
ASI Transmitter
Output Selector
Cable Driver
SMPTE310M VCO Circuit
Quadrature Digital
Up-Converter and DAC
Low Pass Filter