ACTIVE MULTIPLIERS AND DIVIDERS TO SIMPLIFY SYNTHESIZERS

Transcription

1 7 COVER FEATURE ACTIVE MUTIPIERS & DIVIDERS ACTIVE MUTIPIERS AND DIVIDERS TO SIMPIFY SYNTHESIZERS M odern frequency synthesis uses a combination of frequency multiplication and frequency division to generate the required data and carrier signals for microwave radio and radar applications. Frequency multiplication increases the carrier frequency while increasing the phase noise of the carrier by log(n), where N is the multiplication factor. Conversely, frequency division decreases the carrier frequency and changes the phase noise of the carrier by log(/m), where M is the division ratio. For the most part, frequency dividers are used in a phase-locked loop (P) to divide the voltage-controlled oscillator (VCO) output frequency down to the reference frequency in order to achieve phase/frequency locking. These devices are traditionally digital circuits and for high divide ratios (greater than 6) operate at input frequencies less than GHz. At higher frequencies, digital frequency dividers are available in binary division ratios (/, /, /8 ) up to approximately GHz. A new class of GaAs/InGaP heterojunction bipolar transistor (HBT) active frequency dividers offering odd division ratios (/ and /), high input frequency (up to 8 GHz) and wide input power range ( to + dbm) are now available in low cost plastic packages providing the designer with more flexibility in synthesizer architecture. Frequency multipliers, on the other hand, are most commonly used after the VCO to increase the carrier frequency to the radio or radar transmit/receive frequency. Various devices are utilized to achieve frequency multiplication, including Schottky diodes, step recovery diodes, balanced rectifiers (frequency doublers) and saturated amplifiers. The advantages and drawbacks of each approach are well known. A new class of GaAs/InGaP HBT active multipliers offering conversion gain, wide input power range ( to + dbm), high output frequency (up to 6 GHz) and high multiplication factors (, 8 and 6) are now available in low cost plastic packages that will dramatically simplify the design and implementation of X- and Ku-band synthesizers. HITTITE MICROWAVE CORP. Chelmsford, MA Reprinted with permission of MICROWAVE JOURNA from the November issue. Horizon House Publications, Inc. 7 - Alpha Road, Chelmsford, MA 8 Phone: Fax:

2 ACTIVE MUTIPIERS & DIVIDERS 7 INPUT FREQUENCY (GHz) HMC87 HMC89 X X X8 X6 HMC HMC HMC HMC7P HMCP HMCP HMCP OUTPUT FREQUENCY (GHz) VCC RFIN 6 6 RFOUT TOP VIEW PACKAGE BASE Alpha Road, Chelmsford, MA 8 Phone: Fax:

3 7 ACTIVE MUTIPIERS & DIVIDERS OUTPUT POWER (dbm) 6 + dbm dbm dbm OUTPUT POWER (dbm) FREQUENCY (GHz) OUTPUT FREQUENCY (GHz).6 HMC8 SUB HARMONIC MIXER IF OUT R I R I REF P HMC87MS8.7 to GHz HMC7P to 8 to 6 GHz GHz B A IF IN I R I R HMC8 SUB HARMONIC MIXER 7 - Alpha Road, Chelmsford, MA 8 Phone: Fax:

4 (< 8 ma) and low residual phase noise ( to dbc/hz at khz) at frequencies up to GHz. The input and output of the HMC7MS8G and HMC8MS8G dividers feature differential inputs, as V CC IN IN COVER FEATURE Fig. 6 The HMC8MS8G divider s functional block diagram. shown in Figure 6, but can be operated single-ended as well. The low residual output phase noise and wide input power operating range are shown in Figures 7 and 8. The output waveform of the ACTIVE MUTIPIERS & DIVIDERS NC OUT OUT HMC8MS8G divider is shown in Figure 9. The percent duty cycle results in an output frequency spectrum that has low (< dbc) harmonics (Figure ). In sharp contrast, a digital counter set to divide by five typically maintains the input carrier pulse width and hence has approximately a percent duty cycle resulting in the rich harmonics shown in Figure. Since the fifth harmonic of the output is also equal to the input frequency, the HMC8MS8G device has excellent feedthru suppression, as shown in Figure. AN EXAMPE GHz APPICATION A typical application of the HMC7MS8G / divider as an O generator for a mobile phone base 7 SSB PHASE NOISE (dbc/hz) OFFSET FREQUENCY (Hz) 7 POWER (dbc) Fig. 7 The HMC8MS8G divider s SSB residual phase noise at P in = dbm, F in = 6 GHz and T = C. INPUT POWER (dbm) RECOMMENDED OPERATING WINDOW INPUT FREQUENCY (GHz) 9 / / / / / / / / FREQUENCY (NORMAIZED TO INPUT) Fig. Harmonic content of an ideal / divider with percent duty cycle. / / / / / / / / Fig. 8 The HMC8MS8G divider s input sensitivity..... TIME (ns) Fig. 9 Output voltage waveform of the HMC8MS8G / divider at P in = dbm, f out = 88 MHz and T = C. OUTPUT AMPITUDE (mv) POWER (dbc) / / / / / / / / FREQUENCY (NORMAIZED TO INPUT) Fig. Harmonic content of an ideal / counter with percent duty cycle. / / / / / / / / Alpha Road, Chelmsford, MA 8 Phone: Fax:

5 7 OUTPUT EVE (dbm) P feedthrough nd HARMONIC rd HARMONIC INPUT FREQUENCY (GHz) Fig. Output harmonics and feedthrough suppression of the HMC8MS8G / divider at P in = dbm and T = C. station is shown in Figure. O chains for base station applications typically begin with a UHF VCO locked to a crystal frequency source that is frequency multiplied and amplified to the transmit/receive frequency. With the availability of low cost, low noise C-band VCOs and high frequency dividers, the same O signal can be generated by a C-Band VCO and frequency division. In the example shown, a. GHz VCO output directly drives two successive / dividers to create the required 6 MHz O frequency. The entire frequency generation chain consists of three low cost plastic-packaged components with no intermediate amplification or filtering stages. COVER FEATURE 9 REF P ACTIVE MUTIPIERS & DIVIDERS. GHz HMC7 Fig. Base station application block diagram. SSB PHASE NOISE (dbc/hz) The 6 MHz O phase noise is shown in Figure. The VCO phase noise (top curve) is reduced through frequency division by log(/9) = 9 db. At carrier offsets greater than VCO PHASE AT. GHz PHASE NOISE AT 6 MHz DIVIDER PHASE NOISE FREQUENCY (Hz) Fig. Base station O phase noise. 6 6 MHz HMC7MS8G R I MHz, the divider residual phase noise (bottom curve) limits the output phase noise to approximately dbc/hz. CONCUSION A family of active frequency multipliers and frequency dividers has been introduced that allows the synthesizer designer to take new approaches to solving traditional microwave radio and radar application problems. These GaAs/InGaP HBT devices are available in low cost plastic packages operating from single + V supplies. Conversion gain and excellent harmonic/subharmonic suppression minimize external support circuitry. Product samples and connectorized evaluation boards are available on request directly from the factory or online at *Reprinted with the permission of Microwave Journal. 7-6 Alpha Road, Chelmsford, MA 8 Phone: Fax:

6 Notes: ACTIVE MUTIPIERS & DIVIDERS 7 Alpha Road, Chelmsford, MA 8 Phone: Fax: