Motorola has introduced four new integrated circuits that, when combined with an 8-bit controller, provide a complete chipset to implement either a digital or analog CT-900 cordless phone or any of several other 900 MHz ISM band designs. Thought to be the first complete RF analog chipset for low power cordless phone designs available, these units greatly simplify the design process and provide excellent performance upgrades as well.

The four circuits are designed to work together, with the interfaces between the chips fully defined. When compared to the traditional method of using a front-end designed with discrete devices to interface into multiple IF and baseband chips, this new chipset greatly simplifies the designer's task of implementing a new design - and allows use of much more compact PC board layouts.

The units, types MC13145, MC13146, MC33410, and MC33411A, B, provide all of the RF and analog baseband functions needed for analog or digital low power 900 MHz cordless telephones. The only other integrated circuit required to complete a digital or analog CT-900 system is an MC68HC05 microcontroller. All four ICs can be used in three-cell battery powered applications with a power supply voltage as low as 2.7 V, while extending battery life due to low power consumption and power down modes on each IC. Only minimal external components are needed to complete a full CT-900 design. All of these ICs can also be used effectively in a wide variety of Industrial, Scientific and Medical (ISM) band 900 MHz applications as well. For example, the units can be adapted to data applications for either voice or data - and can be modified for use in a Data Radio system - providing a very compelling solution in terms of cost. Typical ISM band applications include wireless LANs, industrial remote controls, and consumer wireless products.

"The MC13145 Receiver and MC13146 Transmitter Subsystems may be used in applications up to 1.8 GHz," said Mark Williams, manager of applications engineering for Motorola's Wireless Subscriber RF/IF Division. "The MC33410 provides the analog baseband functions for a digital 900 MHz system, and the MC33411A or B provides those functions for an analog system."

The MC13145 is a Low Power UHF Wideband Receiver Subsystem consisting of an LNA, two mixers, Voltage Controlled Oscillator (VCO), second Local Oscillator (LO) amplifier, prescaler, IF subsystem, and a coilless detector. This device operates with a supply voltage as low as 2.7 V, and has a current drain of less than 32 mA. A power down mode reduces the standby drain current to less than 50 uA.

The MC13146 Low Power DC to 1.8 GHz Transmitter Subsystem features a linear mixer with linearity control, VCO, and a dual modulus prescaler and exciter. This IC also uses a supply voltage as low as 2.7 V, and has a current drain of 25 mA at 2.0 GHz. Current drain in the powerdown mode is less than 60 uA.

The MC33410 contains a dual CVSD (Continuously Variable Slope Delta Modulator/Demodulator) encoder to digitize speech for RF transmission, and a CVSD decoder to reconstruct the received digital speech from the RF receiver. The MC33410 Dual CVSD/PLL Digital Cordless Phone System also has two PLLs for use with external VCOs and 64/65 or 128/129 dual modulus prescalers. The device also includes a second LO and an independent power amplifier. A serial MCU port is used to control multiple operational features and to adjust low battery and carrier signal detection levels. As with the other devices in the chipset, the MC33410 operates with a supply voltage down to 2.7 V, and has power down modes to conserve power.

The MC33411A and B are 900 MHz Analog Cordless Phone Baseband Systems with a complete expander/compressor for superior noise rejection, two PLLs for use with external VCOs and prescalers, a second LO and dual A/Ds to monitor battery voltage and RSSI. A variety of operational features are controlled through a serial MCU port, and power down modes can conserve power. For more information please visit our website.

Even if Motorola had produced the worst of specifications with this combination chip set it still couldn't fail to take a major share of the market, where the attitude is "lowest price and it works." No, they have done considerably better than that including the capacity for a 150 kbit/s ISM radio: But there a couple of strange things about the set . . .

I really like the analog baseband IC; it is, I think, unique with enough features on both transmit and receive channels to get a lot of product differentials for the market place. The market is still in the analog domain with digital cordless getting really slow acceptance. But the advantage of this chip set is that you can switch to the digital baseband when you want to change the product over -- or run digital production alongside the analog while still having the same RF layouts and testing.

The analog baseband requires external crystal low-pass filters and VCOs/prescalers and my count was 39 components. The receiver unit, the MC13145, requires even more external components including two external IF filters. The input matching into the LNA is particularly horrendous, with four capacitors and one inductor and one wonders why it is so complicated for such a restricted band. The noise figure of the LNA is also poor for 1998 with 3.5 dB typical, 5.0 dB max; these numbers include the first and second mixers but with the gains involved their contribution is low. (Typical numbers being obtained in the 900 MHz band by other vendors are as low as 0.8 dB.) The receiver sensitivity, however, is superb with a 12-dB SINAD of -115 dB. The MC13146 transmit IC is a much cleaner design.

This chipset -- either in digital or analog baseband groupings -- is very much designed to operate as a set and offers little, if no, opportunity to work with other vendors' products. But at the same time there are duplications on the ICs which are strange; there appear to be enough PLLs, for example for three transceivers!

In terms of pricing it maybe should be thought of in terms that a digital radio set would cost $4.54 in 25,000-piece lots while the analog set would cost $3.92. Individually the 145 is $1.50, the 410 $2.12, the 411 $1.50, and the 146 is $0.92. The 146 is in a 24-pin LPQFP while the others are in a 48-pin LPQFP; all are in production. The difference between the 411A and 411B is in the clock source, the "A" version being for where the MCU has its own internal or dedicated clock source allowing the baseband IC to be powered down further.