At the heart of a Sirius receiver is a custom application-specific integrated circuit (ASIC) chip called the "Baseband Integrated Circuit" currently the STA240, which is produced by STMicroelectronics. The chip contains embedded ARM7TDMI and ARM946E-S microprocessors synthesized from IP cores. Every baseband has a unique Electronic Serial Number (or Sirius ID). Another major section of a Sirius receiver is the tuner. The tuner is also a custom ASIC, the STA210. The tuner connects to the antenna, and receives the incoming satellite and terrestrial signals at 2.315 GHz and downconverts them to intermediate frequency signals at around 75 MHz. The strength of the signals is approximately −50dBm in clear-sky conditions. The IF signals are fed to the STA240, which are digitized, demodulated, error-corrected, de-interleaved, and decrypted using specialized circuits on the chip. The baseband processor utilizes a 16MB SDRAM memory to buffer four seconds of one of the satellite signals in order to bring it into time coincidence with the other for Maximal-ratio combining. On newer receivers with a "pause" feature, a dual-port PSRAM is employed to store up to 60 minutes of the selected channel. The baseband processor outputs digital audio over a Serial Peripheral Interface, which is fed to a D/A converter to produce the analog audio signal. The front-end of a Sirius receiver is called the "head unit", required to display descriptive text (such as the category, channel, artist, and song name) and provide controls to the user. This is implemented by the third-party designers of Sirius-ready receivers, using a microprocessor of their choice.