VCR standard audio signal processor

Transcription

1 VCR standard audio signal processor The BA7795LS and BA7795FS are standard audio signal processor ICs. They contain a playback preamplifier, line amplifier, recoeding amplifier, ALC circuit, EQ switch circuit and high-voltage head switch, and provide all of the functions required for normal-audio signal processing on a single IC with a minimum number of external components required. Applications Video cassette recorders and tape decks Features ) Available in compact SZIP and SSOP-A4-pin packages. ) High-with standing-voltage head switch (AC with standing voltage: Min. 80VP-P (f = 70kHz) ). 3) Simple, three-mode EQ switch built-in (BA7795LS). 4) Built-in / TUNER selector switch. 5) High-performance low-noise playback amplifier. Block diagram Input conversion noise figure dbv (Typ. Rg = 680, DIN AUDIO). 6) ALC level can be varied. 7) ALC loop external mute eliminates audible noise at power on, and ALC attack noise. 8) Signal processing circuit can be constructed with the addition of just a few external components. HEAD EQ HSW 3 LP IN 4 GND RIPPLE FILTER 5 VCC 7 6 NFB 8 EQ EQ 9 SP OUT / TU / EE ALC LEVEL 3 IN 5 7 ALC 0dB 4 6 ALC FILTER IN NFB 9 TUNER 8 TUNER IN OUT 0 GND BF OUT EQ 3 0dB BA7795LS 4 / EE The BA7795FS has a different pin layout to the BA7795LS.

2 Absolute maximum ratings (Ta = 5 C) Parameter Symbol Limits Unit Applied voltage VCC 3 V Power BA7795LS 400 Pd dissipation BA7795FS 800 mw Operating temperature Topr ~ 65 C Storage temperature Tstg 55 ~ 5 C Reduced by 4.0mW for each increase in Ta of C over 5 C. Reduced by 8.0mW for each increase in Ta of C over 5 C. Recommended operating conditions (Ta = 5 C) Parameter Symbol Limits Unit Power supply voltage VCC 7.5 ~.5 V Pin descriptions BA7795LS Pin No. BA7795FS Pin No. Pin name Function 7 HEAD EQ Head resonance capacitor switch 8 IN Playback amplifier input / playback head switch 3 9 HSW High-withstanding voltage recording head switch 4 GND GND (playback amplifier) 5 RIPPLE FILTER Ripple filter 6 NFB Playback amplifier feedback 7 3 VCC Power supply 8 4 EQ Playback EQ switch 9 5 EQ EQ control 6 OUT Playback amplifier output 7 / TU / EE / TU / EE control ( / EE control) 8 IN Playback line amplifier 3 9 ALC LEVEL ALC level setting 4 0 ALC FILTER ALC filter time constant 5 Bias 6 IN Line input 7 3 control 8 4 TUNER IN Tuner input ( / EE control) 9 NFB Recording amplifier feedback 0 GND GND 3 OUT Recording amplifier output 4 BF OUT Line amplifier output 3 5 EQ Recording EQ switch (recording EQ switch ) 4 6 / EE / EE control (recording EQ switch )

3 Electrical characteristics (unless otherwise noted, Ta = 5 C, VCC = 9V, and f = khz) Parameter Symbol Min. Typ. Max. Unit Conditions Quiescent current EE IqEE ma When no signal Quiescent current Iq ma When no signal Quiescent current Iq ma When no signal Line amplifier Power supply gain ( input) GVCP db VO = V Power supply gain (,, TU inputs) GVCL db VO = V Distortion THDL % VO = V, RL = Ω Maximum output level VOmL dbv THD = %, RL = Ω Output residual noise VNOL dbv Rg = Ω, DIN AUDIO ALC level ALC distortion Mute attenuation ratio Recording amplifier Voltage gain Distortion Maximum output level Open loop gain Playback preamplifier Open loop gain Input conversion noise Total gain Head switch head switch impedance head switch impedance head switch AC withstanding voltage Measured at BW = 400Hz to 30kHz. VOA dbv VIN = 3dBV R / R = 8. / 39kΩ THDA % VIN = 3dBV, RL = Ω MT db Vo = 0dBV, DIN AUDIO GVCR db, TUNER input OUT THDR % VO = V VOmR dbv VO = V, RL = Ω GVOR db THD = %, RL = Ω GVOP 6 68 db VNINP.5 4 dbv Rg = 680Ω, DIN AUDIO GVCP-L db IN BF OUT RPH 0 Ω RRH 0 Ω BVRHAC 80 0 VP-P f = 70kHz 3

4 Input / output circuits kω EQ 56kΩ / TU / EE / EE 56kΩ 56kΩ Fig. HSW 4

5 Measurement circuit BA7795LS AC IN k µ 3 5 LP 4 3.3µ k 680 ON: GVO µ IN VCC 33µ 7 6 k 330k 0.0µ 8 EQ 9 SP 8.k / TU / EE R 3 47µ R 4.M 5 7 ALC 8dB 6 ON: ALC OFF IN ON: GVE.5k 9 TUNER 8 TUNER IN OUT 0µ 5k 0 µ 3 0dB BF µ RL OUT 4 / EE Units: R [Ω] C [F] The BA7795FS has a different pin layout to the BA7795LS. Fig. 5

6 Circuit operation () EE oparation The input switch is used to select the audio signal input source ( or TUER). This signal is amplified by the line amplifier (voltage gain: 0dB at khz). The ALC circuit controls the line amplifier output level. The ALC level is set externally. If mute mode is set in this state, the switch that connects the output buffer will go off, but the ALC loop will not be cut. () Recoeding In recording mode, the recording amplifier directly connected to the line amplifier operates. The HEAD switch in the playback equalizer amplifier block switches on, and the signal is not input to the playback equalizer amplifier. The line amplifier output is attenuated by 0dB before it is input to the recording amplifier, so if the feedback components are chosen to given a gain of 0dB, the same OUT output level as the line amplifier can be obtained. It is also possible to switch the equalizer characteristic to suit the tape speed by switchig the control signal to EQ. The recording amplifier gain and equalizer characteristics are set externally. Signal flow for EE and recording operation LP 3.3µ µ 3 4 µ VCC 33µ k 0.0µ EQ / TU / EE 9 8 k 8.k 39k 3 47µ 8.k 5 ALC 4.M 7 8dB 6 IN.5k 9 8 TUNER IN 5k 0 RL OSC B 3 BF OUT 0dB µ / EE 4 BA7795LS Units: R [Ω ] C [F] The BA7795FS has a different pin layout to the BA7795LS. Fig. 3 Signal flow for EE / recording 6

7 (3) Playback operation The signal applied to IN is amplified by playback equalizer amplifier. At this time, the HEAD switch is switched on by a control signal to / EE, and the potential on one side of the head is fixed at GND. The playback equalizer amplifier gain and equalizer characteristics are set externally. The playback level is set by the resistor divider between OUT and the playback line input, The signal to the playback line input passes though the input switch, is amplified by 0dB in the line amplifier, and is output to the output buffer (the voltage gain is different to that for the input and TUNER input). It is possible to switch between the input block head equalizer resonance point and playback equalizer characteristic using the EQ control signal. The line output can be stopped by setting muting mode on using the signal. The ALC circuit and recording amplifier are stopped in playback mode. Signal flow for playback operation µ 33µ 3 5 LP 4 3.3µ µ 330k VCC k 0.0µ EQ 9 SP 8 8.k k / TU / EE 39k 3 47µ 8.k 5 7 ALC 8dB 4 6.M IN.5k 9 8 TUNER IN OSC µ 5k 3 0dB BA7795LS BF 0 4 µ OUT / EE B Units: R [Ω] C [F] The BA7795FS has a different pin layout to the BA7795LS. Fig. 4 Signal flow for playback 7

8 Control mode table () / EE, / TU / EE Control pins Function Mode / EE / TU / EE HSW HSW SW AMP L L Mode OFF ON OFF L M TUNER OFF ON TUNER OFF L H OFF ON OFF H L ON OFF ON H M TUNER ON OFF TUNER ON H H inhibit If / EE is set to "M", the pause state is possible ( head switch: open, amplifier: off). () Control pins Function Mode H SW OPEN L CLOSE (3) EQ Control pins Mode Function E Q MODE 3 MODE HEAD EQ SW EQ SW EQ SW L SP SP OFF CLOSE OFF M LP ON OPEN OFF H ON OPEN ON The L, M and H thresholds are: L to M:.7V, L to H:.5V, and M to H: 3.3V. 8

9 Application example (BA7795LS) VCC 3 33µ 5 µ µ 7 LP µ 330k µ EQ / TU / EE 9 SP 8 8.k k R 3 47µ OSC R.5k 5k dB ALC 8dB BF TUNER µ.m RL IN TUNER IN OUT / EE B Units: R [Ω] C [F] The BA7795FS has a different pin layout to the BA7795LS. Fig. 5 9

10 Operation notes () ALC level Set the ALC level in the range V to 0dBV by selecting the values of resistors R and R connected between, ALC LEVEL and GND. The formula for approximating the value of this resistor is as follows: () Mute signal Apply the mute signal shown below at power on and off. If the muting time is short, a pop sound will be audible, particularly when the power is switched on. VOA = = R VCC 0.7 R R R V R R (H) sec or more (H) VCC OUT If the ALC level setting is too low, level variation will increase compared to that of the standerd level (VOA = 6dBV), and conversely, if the level is too high, the level variation will decrease, but distortion will increase.there is almost no temperature characteristic, but the ALC level does vary with supply voltage (VCC) as shown in the formula above. Use care when setting it. Fig. 7 Also, be certain to apply the mute signal when switching between / / TU. In the case of / TU switching, it is possible to suppress switching noise by applying a time constant to the signal, in which case it is not necessary to apply the mute signal. (3) Recording control Do not switch the and modes on togther. This will cause faulty operation. V = VCC 0.7 R R R V Fig. 6 ALC LEVEL (4) Line output The line output can drive a load resistance of up to kω. Depending on the type of load, it can cause local oscillation (eg. large capacitive loads that draw large current), so caution is required. In particular, when there is a possibility that the line output will be connected to a shielded cable, or line cable, connect a resistor of about kω in series with the output so that the capacitive load is not directly coupled to the IC output terminal.

11 Electrical characteristic curves GAIN: GVCLT (db) VCC = 9V ALC; OFF 0 k k 0k M FREQUENCY: f (Hz) Fig. 8 Gain vs. frequency ( amplifier) OUTPUT LEVEL: VOA (dbv) 0 0 VCC = 9V f = khz R kΩ R = kω R = 8kΩ R = 39kΩ INPUT LEVEL: VIN (dbv) Fig. 9 Line amplifier ALC input / output characteristics MAXIMUM OUTPUT LEVEL: VOmL (dbv) VCC = 9V (ALC; OFF) f = khz THD = % (0.4 ~ 30kHz) µ RL k k 5k k OUTPUT IMPEDANCE RL (Ω) Fig. Line amplifier load drive characteristics GAIN: GVOP GVC (db) SW GVO k 330k k 0.0µ 330 µ BA7795LS (SW: OFF) SP (SW: ON) 0 k k 0k M M OUTPUT LEVEL: VO (dbv) VCC = 9V ALC; OFF DIN AUDIO TU 0 k k 0k OUTPUT NOISE LEVEL: VON (dbv) DIN AUDIO VCC = 9V CIN = 4.7µF k k 5k k FREQUENCY: f (Hz) FREQUENCY: f (Hz) INPUT IMPEDANCE: Rg (Ω) Fig. Playback amplifier frequency characteristics Fig. Line amplifier crosstalk Fig. 3 Playback amplifier output noise characteristics

12 External dimensions (Units: mm) BA7795LS BA7795FS.8 ± 0..8 ± 0..0 ± ± ± ± Min ± ± ± ± ± Min. 0.5 ± SZIP4 SSOP-A4