The 4100 was (According to Wikipedia) the last SD set-top box that Bell used, getting discontinued in 2012.
On the board we have:-
Mystery Chip? NC206B2B 144138 =045794524458
Cirrus Logic – CS4335K 24 bit 96kHz Stereo D/A Convertor
ST Viper 53 – Off-line primary switch
Also on the board but not annotated up is a Philips 74HCT08 (Quad And Gate) an ST LM358 Op Amp, an unknown chip labelled CNY-17F and an another 24AA64 (Possibly a small serial Flash). A lot of Conexant silicon on this board.
Also on the board is the information “Designed in the UK 2005” and “Asssembled in Mexico”. Given the UK design I wonder if this this box (or variant) was also be used by BSkyB in UK which was/is a big Satellite TV system.
Lets look at the silicon starting with the RF “Satellite In” connection. Reading up about this, the very high C-band (4-8GHz) or Ku-band (12-18GHz) satellite signal is downconverted to L-band (950MHz -2125MHz) by an LNB (Low noise block downconverter) in the feedhorn of Parabolic dish. That looks like something worth tearing down, I will add it to my list of stuff I want to look out for!
CX24109 Satellite TV Tuner
This is quite an advanced Bipolar process with small geometry metal tracks. The layout looks quite interesting with several distinctive blocks visible. A datasheet exists for this part and indicates how much is going on. It consists of an LNA, variable RF attenuator, quadrature downconverter, variable IF gain amplifiers, variable low-pass filters, VCO, and synthesizer.
You can see 7 instances of this circuit using two inductors connecting to interdigitated finger MIM capacitors and some resistors and other capacitors – this may be an impedance matching circuit or possibly an LNA circuit
The Bipolar transistors used all seem to be dual emitter configurations, with circular emitters, octagonal base, with a minimum (That I could find) 2 emitters per collector. Here you can see single collector two emitter transistors, together with single collector 8 emitter transistor configuration.
CX24123 QPSK Demodulator
This is the RF tuning -demodulation block diagram from the CX24109 datasheet
You can see the output of the the tuner IC goes directly into the CX24121 – in our case it is a CX24123.
CX24153 MPEG 2 Decoder
From the QPSK demodulator the signal is fed to a CX24153 MPEG 2 decoder chip, the biggest device on the board that is connected with Flash and DRAM memory. This BGA (Ball Grid Array) mounted device has a 6.2mm x 5.92mm die inside. Again made on a (estimated) 180nm CMOS process
Once the signal is converted to MPEG 2 it is put directly into the the TV out circuitry, which is just a bunch of discrete devices (Impedance matching to reduce insertion loss).
CX86500 and CX20493
The CX86500 modem chip and CX20493 digital isolation barrier/line interface are circuitry used to allow phone line interconnection to the board (Given the acronym DAA-Data Access Arrangement) as per this implementation
Its fabbed on a 0.25μm CMOS process and you can see has a mix of digital and mixed signal analog circuitry. You can see a lot of on chip capacitors in the die photo. However not sure you can make out any real functionality here.
The 86500 modem chip is a bit boring really just a 5.08mm x 2.7mm digital die.
Lastly tucked away in the top left corner of the board next to the power supply components is the strangely marked thin BGA.
I think what we have here is a secure MCU. This is the chip that descrambles the signal encryption. The vendor goes to great length to prevent reverse engineering the meandering track is designed such that if it is broken (By delayering) then the chip cannot function.
The last part of the mystery. Why is this chip located in the corner with the power supply? I would expect it to be associated with the MPEG decoder (Or the QSPK demodulator.) If you look at the corner of the board you can see the (output of this) secure MCU is connected to a 14 pin ic. Which on inspection is a 7400 series logic chip, in fact the 74HCT08 a quad AND gate! Which I blogged about last week
Why on earth would you connect a 32 bit MCU through 4 AND gates??!